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Metal-support interaction enhanced electrochemical reduction of CO2 to formate between graphene and Bi nanoparticles
Journal of CO₂ Utilization 37 (2020) 353–359
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Journal of CO2 Utilization journal homepage: www.elsevier.com/locate/jcou
Metal-support interaction enhanced electrochemical reduction of CO2 to formate between graphene and Bi nanoparticles
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Dan Wua, Wenyue Chena, Xuewan Wanga, Xian-Zhu Fua,*, Jing-Li Luoa,b,** a b
College of Materials Science and Engineering, Shenzhen University, 1066 Xueyuan Ave., Shenzhen, China Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, T6G 1H9, Canada
A R T I C LE I N FO
A B S T R A C T
Keywords: Metal-Support interaction Bismuth CO2electroreduction Graphene Formate
Metal nanoparticles stabilized on a support material have been explored extensively to boost heterogeneous catalysis. Herein, the effect of metal-support interaction between bismuth (Bi) nanoparticles and reduced graphene oxide nanosheets (Gr) on the electroreduction of CO2 towards value-added formate is explored. The obtained Bi/Gr hybrid catalysts exhibit a superior catalytic activity towards electrochemical reduction of CO2, which gives the maximum faradic efficiency of 92.1 % at -0.97 V (vs. RHE) for formate generation. Particularly, the hydride shows an enhancement to the catalysts of bare Bi and physical mixture of Bi and Gr, with a high current density of 28.1 mA∙cm−2 and production rate of 0.53 mol∙cm−2 h-1 at -1.17 V (vs. RHE) for formate generation. The electrochemical analysis reveals that the metal-support interactions substantially boost CO2 electroreduction activity through modification the electronic structure and improving interfacial electron transfer between Bi and Gr. This work not only deepens an understanding of metal-support interaction effect but also sheds light on the design of high-efficiency catalysts toward CO2 electroreduction by virtue of the interactions between active metals and carbon-like support.
1. Introduction The worldwide overproduction of carbon dioxide (CO2) brings about serious environmental pollution and climate change issues. In this regard, electrocatalytic conversion of CO2 to value-added chemicals is regarded as a prospective pathway for simultaneous recycling of carbon resource and the generation of energy-rich fuels [1,2]. Among various CO2 reduction chemicals, formic acid (FA) is a promising nonflammable energy-storage liquid media and a natural biomass for the sustainable development of human civilization [3,4]. Taking the advantage of two-electron reduction process, less energy input is required to overcome the kinetic barriers for FA generation compared to the higher order CO2 reduction products which needs activating multielectron transfers. To this end, numerous improvements are devoted to various electrocatalysts to simultaneously achieve desirable catalytic activity and FA selectivity. Substantial experimental and theoretical efforts have been documented that certain metal electrocatalysts, such as Pd, Sn, Pb, Bi, In and Cd, can selectively make FA from CO2 [5–7]. Owing to the merits of cost-effectiveness and eco-friendliness, metallic Bi has been considered as a promising candidate for electrochemical conversion of CO2 to FA
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compared to noble and toxic metals. Currently, the electrocatalytic activity and FA selectivity of Bi is regulated by different features, including particle size [8,9], morphology [4,10,11], defect [12–15], and so forth. Beyond these intrinsic characteristics, immobilizing Bi nanoparticles on the support matrix to improve the stability and control the spatial distribution is one of the critical strategies. The so-called strong interaction between metal and substrate (metal-support interaction) also offer great opportunities for the improvements of electrocatalytic performance [16–18]. However, the metal-support interactions can also give rise to new interfacial phenomena. Therefore, controlling this interaction to optimize the electrocatalytic activity are highly desired. Generally, various types of catalyst support have been developed to immobilize metal nanoparticles, such as carbon materials, oxides and nitrides [19–21]. Particularly, graphene, a typical two-dimensional carbon material, is considered as an ideal platform for metal catalysts, which is featured with large surface area, high conductivity and good stability [18]. In this regard, immobilizing metal nanoparticles on graphene support prohibits the aggregation of particles by controlling their spatial distribution. Moreover, the graphene nanosheets supported open structure enables fully exposed active sites to adsorb and activate CO2 molecules, thus further contributing to enhanced overall
Corresponding author. Corresponding author at: College of Materials Science and Engineering, Shenzhen University, 1066 Xueyuan Ave., Shenzhen, China. E-mail addresses: [email protected] (X.-Z. Fu), [email protected] (J.-L. Luo).
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https://doi.org/10.1016/j.jcou.2020.02.007 Received 27 November 2019; Received in revised form 8 February 2020; Accepted 10 February 2020 2212-9820/ © 2020 Elsevier Ltd. All rights reserved.
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electroactivity and durability [22]. More importantly, the interface between metal nanoparticles and the support can give rise to a redistribution of electrons with noticeable effects [23]. In general, electron transfer is observed once metal nanoparticles contact with the support to facilitate the charge transfer and further improve the catalytic activity. As a result, coupling Bi nanoparticles with graphene nanosheet support is expected to bring many possibilities to improve the catalytic activity and stability in the electrochemical CO2 reduction process. In this work, Bi nanoparticles are uniformly deposited on reduced graphene oxide nanosheets (Gr) via a simple hydrothermal method. The metal-support interaction between Bi nanoparticles and Gr nanosheet substrate is confirmed. The influence of metal-support interaction on the catalytic activity and FA selectivity for electroreduction of CO2 on Bi/Gr hybrid is fully explored. Such interaction induced enhancement is revealed by experimental results and electrochemical analysis. 2. Experimental section
Fig. 1. XRD patterns of Bi/Gr and pure Bi samples.
2.1. Synthesis of Bi/Gr
separately purged into anodic and cathodic counterparts under mild stirring at 500 rpm throughout the experiments. During the electrolysis, CO2 delivered to the cathodic counterpart was routed into gas chromatography (GC, Fili, 9790Plus) equipped with a TCD detector and an FID detector to monitor the gas products. The KHCO3 solution after electrolysis was collected and analyzed on an ion chromatograph (IC, Shenghan, CIC-D120) to quantify liquid products.
Graphene oxide (GO) was prepared by using a modified Hummers method as described in Supporting Information. In a typical synthesis of Bi/Gr, 10 mg Bi(NO3)3 was added to 10 mL of GO (1 mg mL−1) with further ultrasonication for 20 min to form a uniform suspension. Subsequently, 5 mL of hydrazine hydrate (85 wt%) was added into the suspension and the solution pH was adjusted to 11 using aqua ammonia (28 wt%). After stirring for 30 min, the mixture was transferred into a Teflon-sealed autoclave at 120 °C for 18 h and then naturally cooled down to room temperature. After washing with DI water and ethanol several times, the product was freeze-dried for 24 h and the product was denoted as Bi/Gr. For comparison, a series of samples was also prepared by the same procedure expect for different addition amount of Bi(NO3)3 precursor. The obtained catalysts were denoted as 0.1Bi/Gr, 0.5Bi/Gr and 3Bi/Gr, respectively, when the mass ratio of Bi(NO3)3/GO precursor was 0.1, 0.5 and 3. The pure Bi nanoparticles and Gr nanosheets were also prepared through the similar procedure respectively in the absence of GO and Bi(NO3)3. The physical mixture of Bi nanoparticles and Gr nanosheets (Bi-Gr) was also obtained for comparison.
3. Results and discussion Fig. 1 shows the XRD patterns of the obtained samples. All the diffraction peaks of Bi/Gr can be assigned to the rhombohedral phase of Bi (PDF 00-044-1246). No observable peaks related to bismuth oxide are found, evidencing high phase-purity of Bi/Gr. Moreover, no discernible the diffraction peaks of Gr can be observed, probably due to the relatively low diffraction intensity of Gr in the hybrid. Noticeably, the insert shows a clear peak shift of Bi/Gr compared to the pure Bi, suggesting the alteration of interlayer spacing of layer Bi crystal structure induced by a strong interaction between Gr support and Bi particles. GO with negatively charged oxygen-containing functional groups can facilitate the coordination with positively charged Bi3+ ions. A further hydrothermal treatment results in a further simultaneous reduction of GO and Bi3+ ions. Furthermore, the hydrazine-involved redox can yield N2 gas, which can create an inert atmosphere and thus prevent the Bi NPs from re-oxidation in the aqueous solution, resulting in the formation of Bi/Gr hybrids. According to the ICP-OES measurement, the Bi loading in Bi/Gr hybrid is determined to be 41.2 wt%. The chemical coupling also can also greatly affect the surface chemistry of materials. XPS spectra were carried out to probe the elemental chemical state. The high-resolution of C 1s spectra in Fig. 2a can be deconvoluted into a dominated peak for CeC/C = C/C–H bond at 284.7 eV, along with weak peaks of C]N bond at 285.6 eV, CeO/C-N bond at 286.9 eV, C]O bond at 288.4 eV and HOeC = O bond at 290.7 eV, respectively. The dominated sp2-bonded carbon atoms suggest a high carbonization degree of Bi/Gr and an excellent conductivity for the catalysts could be expected. The N 1s XPS spectra (Fig. 2b) of Bi/ Gr is fitted into three typical peaks corresponding to the graphitic N (401.9 eV), the pyrrolic N (399.8 eV) and the pyridinic N (ca. 398.3 eV). Besides the decreased overall N content, the graphitic N content in Bi/ Gr catalysts increases while the pyridinic N content is reduced at relatively low levels compared to the Gr sample (Table S1). This is because the introduction of Bi heteroatoms disrupts the configurations of bulk Gr nanosheets, resulting in a decreased graphitic N and more edges available for the formation of pyridinic N [24,25]. Moreover, the pyrrolic N is the primary N bonding state in Bi/Gr and Gr catalysts whereas the binding energy of graphitic N and pyridinic N in Bi/Gr shift in comparison with that of Gr, which is ascribed to the changes of N-
2.2. Characterizations The X-ray diffraction (XRD) pattern were recorded on a SmartLab (Rigaku) diffractometer. The morphology of samples was obtained on a high-resolution transmission scanning electron microscope (HRTEM, JEM-F200). The Raman spectra were recorded using a Raman microscope (LabRam HR, Horiba evolution). The XPS data were obtained from a K-Alpha X-ray photoelectron spectrometer (Thermo Scientific). The mass loading of Bi in the hybrid was determined by an inductively coupled plasma optical emission spectrometer (ICP-OES, Perkin Elmer Optima 2100 DV). 2.3. Electrochemical measurements The electrochemical measurements were conducted using a H-type reactor on a three-electrode system using Pt foil as the counter electrode and Ag/AgCl as the reference electrode. Typically, 5 mg of Bi/Gr catalysts was added to a mixture of 950 μL ethanol and 50 μL Nafion solution (5 wt%), and sonicated for 1 h to form a homogeneous catalyst ink. Then, the catalyst ink was uniformly air-brushed onto a 1 × 1 cm2 carbon paper with a mass loading of 1 mg∙cm−2 to act as the working electrode. All potentials measured against Ag/AgCl electrode were converted to the RHE scale using equation of ERHE= EAg/AgCl + 0.197 V + 0.0591 × pH. The electrochemical reduction of CO2 was carried out in CO2-saturated 0.5 M KHCO3 electrolyte (pH = 7.3) at room temperature. Highpure CO2 at a flow rate of 20 mL min−1 was continuously and 354
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Fig. 2. High-resolution XPS spectra of (a) C 1s, (b) N 1s, (c) Bi 4f and (d) Raman spectra of samples.
interplanar spacing of 0.32 nm correspond to the (012) planes of rhombohedral Bi phase (Figs. 3b and S2), which is the low-energy facet of Bi [11]. This suggests that contact with the support can prevent the agglomeration and growth of Bi nanoparticles and lower the surface energy of Bi nanoparticles planes, favoring sphere shapes over others [26]. The EDX spectra (Fig. 3c) also verifies the homogenously immobilization of Bi on the Gr support matrix. The electrochemical activity of CO2 reduction on Bi/Gr catalyst is evaluated in a three-electrode system using a proton membrane separated H-type reactor. The LSV curves of Gr/Bi in Ar or CO2 saturated 0.5 M KHCO3 electrolyte are shown in Fig. 4a. Obviously, Bi/Gr catalysts exhibit significantly higher current density (j) in the CO2 saturated electrolyte than that in the Ar purged one at the same potential, indicating that Bi/Gr can effectively promote CO2 reduction and conversion with unfavorable hydrogen evolution reaction. Fig. 4b reports the faradaic efficiencies (FEs) as a function of cathodic potentials. For Bi/Gr catalysts, the liquid HCOOH is found as the major reduction product with minor gaseous H2 and negligible CO for CO2 electroreduction. The HCOOH is initially detected at -0.57 V (vs. RHE). The FE for HCOOH (FEHCOOH) rapidly increases and achieves the maximum value of 92.1 % at -0.97 V (vs. RHE). The FEHCOOH is further compared between bare Bi and Gr (Fig. 4c). No detectable HCOOH is found for Gr, suggesting that Bi is the active phase toward HCOOH generation in CO2 electroreduction. The FEHCOOH on Bi-Gr (the physical mixture of Bi nanoparticles and Gr nanosheets) is much lower than Bi/Gr at identical operating potentials. The highest FE is 83.2 % at -0.97 V (vs. RHE) with a sharp drop at more negative potentials. And similar spectral profile with slightly decreased FEHCOOH is observed for bare Bi sample. The
bonding configurations for two samples. As shown in Fig. 2c, the binding energies centered at 158.2 eV and 163.5 eV corresponds to Bi° and the shoulders situated at higher binding energies of 159.3 eV and 164.8 eV are assigned to Bi3+ in Bi/Gr composites. Comparatively, the bare Bi nanoparticles without support also have two doublets peaks related to Bi3+ and metallic Bi, but with different spectral profiles. The oxidized species are probably resulted from the surface oxidation of Bi nanoparticles during the characterizations. The above results evidence that the electronic structure of Bi and Gr in the hybrid is changed through the strong mutual interaction. The interface between a metal nanoparticle and the support matrix can give rise to a rearrangement of electrons within both materials [23,26]. Further surface information about the catalyst can be also obtained from Raman spectroscopy (Fig. 2d). For Bi/Gr catalysts, the peaks located at 64.5 and 89.9 cm−1 are referred to the characteristic Eg mode and A1g mode peaks of metallic Bi [4,27], while the doublet peaks at about 1330 and 1600 cm−1 are respectively accounted for the typical D and G bands. These peaks in the hybrids slightly shift compared with its bare counterparts, resulting from the metal-support interaction effect. Additionally, a weak peak at around 180 cm−1 attributing to the surface oxidation is found for both Bi and Bi/Gr samples, which is corresponded to the XPS results. The ultrathin nanosheet characteristic endows GO as perfect support substrate to disperse Bi ions (Fig. S1). The morphology of the representative Bi/Gr catalysts is characterized. The TEM image (Fig. 3a) shows that small Bi nanoparticles are uniformly dispersed on the Gr nanosheets without observable aggregation. The average size of the Bi nanoparticle is about 5 nm. A closer observation in Fig. 3b clearly exhibits the lattice fringes of Bi and Gr. The lattice fringes of an 355
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Fig. 3. (a) TEM, (b) HRTEM images and (c) EDX mappings of Bi/Gr sample.
Fig. 4. (a) LSV curves for Bi/Gr in Ar and CO2 saturated 0.5 M KHCO3, (b) FEs for Bi/Gr catalysts, (c) HCOOH faradic efficiencies (FEHCOOH) for Gr, Bi, Bi-Gr and Bi/ Gr catalysts, and (d) long-term satiability test at -0.87 V (vs. RHE) for 30 h on Bi/Gr catalysts. 356
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Fig. 5. (a) Partial current density and production rate for HCOOH production and (b) corresponding Tafel slops for Bi, Bi-Gr and Bi/Gr catalysts.
jHCOOH goes up first and then declines with the Bi3+/GO mass ratio rising from 0.1–3. Overall, the Bi/Gr catalysts show the best electrocatalytic CO2 reduction activity in terms of HCOOH selectivity and current density. This phenomenon is related to the morphological change of Bi nanoparticles in the hybrid. As demonstrated in Fig. S4, highly dispersed Bi nanoparticles in the 0.1Bi/Gr and 0.5Bi/Gr hybrid are less than 1 nm in size while aggregation and large bulk of Bi nanoparticles can be observed in the 3Bi/Gr hybrid. Since the Bi is the active phase towards HCOOH generation in CO2 electroreduction, less Bi addition or aggregation of Bi nanoparticles would reduce the active sites. Moreover, the generated reduction products of CO and H2 probably cover on the surface of ultra-small Bi nanoparticles, which is unfavorable for its interaction with CO2 molecules in the electrochemical CO2 conversion process. More importantly, A synergy can be created at the interface for the combination of Bi and Gr, which thus accelerates CO2 adsorption, intermediate binding and stability, benefiting CO2 to HCOOH conversion [29,30]. However, the metal-support interaction effect is attenuated for larger Bi nanoparticles because of the reduced impact of charge transfer and relatively reduced metallic surface area in intimate contact with the support [31]. Therefore, Bi/Gr hybrid with Bi nanoparticles in appropriate size is expected to exhibit the best electrocatalytic performance for CO2 reduction.
above results indicate that the strong interaction between Bi and Gr can enhance the HCOOH selectivity in electrochemical CO2 reduction. The long-term durability test of Bi/Gr illustrated in Fig. 4d shows negligible decays of the current density at -0.87 V (vs. RHE) over 30 h, manifesting a remarkable stability of Bi/Gr electrocatalysts. The in-depth understanding for the contribution of the metal-support interaction to the enhancement of electrochemical CO2 reduction activity is disclosed. The partial current density for HCOOH generation (jHCOOH) and HCOOH production rate on bare Bi, Bi-Gr and Bi/Gr catalysts are plotted in Fig. 5a. Overall, the Bi/Gr exhibits a much higher jHCOOH across potentials from -0.57 V (vs. RHE) to -1.17 V (vs. RHE). In contrast, the bare Bi and Bi-Gr catalysts show much lower jHCOOH with similar trend in CO2RR. More specifically, Bi/Gr reaches a maximum jHCOOH value of -28.1 mA∙cm−2 at -1.17 V (vs. RHE), which is higher than a maximum jHCOOH value of 7.9 and 14.1 mA∙cm−2 for Bi and Bi-Gr at the same cathodic potential. Simultaneously, the higher production rate is also expected for Bi/Gr catalysts. As evidenced in Fig. 5a, the HCOOH generation rate rapidly increases with more negative potentials to achieve 0.53 mol∙cm−2 h-1 at -1.17 V (vs. RHE), which is higher than that of Bi-Gr with a value of 0.26 mol∙cm−2 h-1 at -1.17 V (vs. RHE). The bare Bi gives a maximum value of 0.16 mol∙cm−2 h-1 at -1.07 V with subsequent decline at -1.17 V (vs. RHE). The results demonstrate that the metal-support interaction can facilitate the surface charge transfer between Bi and Gr, favoring for the CO2 reduction. Tafel analysis offer valuable insights into reaction mechanisms. As calculated in Fig. 5b, the Tafel slops of Bi, Bi-Gr and Bi/Gr catalysts are 185, 167 and 152 mV dec-1, respectively. These values are close to the theoretical value of 118 mV dec-1, suggesting the initial electron transfer or proton-coupled electron transfer is the rate limiting step in CO2 electroreduction process [28]. The smallest Tafel slop of Bi/Gr implies its fastest reaction kinetics. Based on the above analysis, Bi/Gr with two-dimensional nanostructure offer more active site for CO2 adsorption and the strong interaction can improve interfacial charge-transfer, which is advantageous for the subsequent CO2 activation and conversion to HCOOH, resulting in enhanced electrochemical activity in CO2RR. The influence of the Bi nanoparticle loading mass in the hybrid on the HCOOH generation is also investigated. The Bi amount in the 0.1Bi/ Gr, 0.5 Bi/Gr and 3Bi/Gr hybrid is measured to be 4.6 wt.%, 20.9 w.t.% and 93.6 wt.%, respectively. As shown in Fig. 6a, the overall FEHCOOH of hybrid increases across the tested negative potentials ranging from -0.57 V (vs. RHE) to -1.17 V (vs. RHE) when the Bi loading amount increases in succession from 0.1Bi/Gr, 0.5 Bi/Gr to Bi/Gr catalysts. However, when further increasing the Bi loading, the overall FEHCOOH of 3Bi/Gr catalysts drops. The profiles of total current density for these catalysts are plotted in Fig. S3. Accordingly, the partial current density for HCOOH generation (jHCOOH) is calculated. The evolution of jHCOOH with different loading of Bi follows similar trend (Fig. 6b). The value of
4. Conclusions Bi/Gr hybrids are synthesized with the construction of metal-support interaction between Bi nanoparticles and ultrathin Gr nanosheets. This interaction can considerably improve the electrochemical performance of CO2 reduction, resulting in high faradic efficiency over a wide negative potential range. In specific, Bi/Gr gives a current density of 28.1 mA∙cm−2 and production rate of 0.53 mol∙cm−2 h-1 at -1.17 V (vs. RHE) for formate generation, which is about 2 times higher than those of physically mixed Bi-Gr samples. The precursor Bi3+/GO ratio also affects the faradaic efficiency and current density for formate production. The kinetically experimental evidence reveals that the strong metal-support interaction mainly attributes to the enhanced electrochemical CO2 reduction activity by improving the interfacial electron transfer ability. We believe the present work provides a promising alternative strategy for metallic Bi to maximize the catalytic activity toward electroreduction of CO2 into value-added formate. CRediT authorship contribution statement Dan Wu: Conceptualization, Methodology, Validation, Formal analysis, Writing - original draft, Project administration. Wenyue Chen: Investigation. Xuewan Wang: Resources, Funding acquisition. Xian-Zhu Fu: Resources, Writing - review & editing, Visualization, 357
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Fig. 6. (a) FEHCOOH and (b) jHCOOH of 0.1Bi/Gr, 0/5Bi/Gr, Bi/Gr and 3Bi/Gr catalysts.
Funding acquisition. Jing-Li Luo: Resources, Supervision. [10]
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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Acknowledgements This work was financially supported by the National Natural Science Foundation of China (No. 21975163and51902204) and Bureau of Industry and Information Technology of Shenzhen (No. 201901171518). The authors would like to acknowledge the technical support provided by Instrumental Analysis Center of Shenzhen University (Xili Campus) and thank Yang Chengyu from Shiyanjia Lab (www.shiyanjia.com) for the XPS experiments.
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Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.jcou.2020.02.007.
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References
[18]
[1] W.J. Zhang, Y. Hu, L.B. Ma, G.Y. Zhu, Y.R. Wang, X.L. Xue, R.P. Chen, S.Y. Yang, Z. Jin, Progress and Perspective of Electrocatalytic CO2 Reduction for Renewable Carbonaceous Fuels and Chemicals, Adv. Sci. 5 (2018) 1700275. [2] M.G. Kibria, J.P. Edwards, C.M. Gabardo, C.T. Dinh, A. Seifitokaldani, D. Sinton, E.H. Sargent, Electrochemical CO2Reduction into Chemical Feedstocks: From Mechanistic Electrocatalysis Models to System Design, Adv. Mater. 31 (2019) 1807166. [3] B. Jiang, X.G. Zhang, K. Jiang, D.Y. Wu, W.B. Cai, Boosting Formate Production in Electrocatalytic CO2 Reduction over Wide Potential Window on Pd Surfaces, J. Am. Chem. Soc. 140 (2018) 2880–2889. [4] D. Wu, J.W. Liu, Y. Liang, K. Xiang, X.Z. Fu, J.L. Luo, Electrochemical Transformation of Facet-Controlled BiOI into Mesoporous Bismuth Nanosheets for Selective Electrocatalytic Reduction of CO2 to Formic Acid, ChemSusChem 12 (2019) 4700–4707. [5] J.E. Pander, M.F. Baruch, A.B. Bocarsly, Probing the Mechanism of Aqueous CO2Reduction on Post-Transition-Metal Electrodes using ATR-IR Spectroelectrochemistry, ACS Catal. 6 (2016) 7824–7833. [6] R. Hegner, L.F.M. Rosa, F. Harnisch, Electrochemical CO2Reduction to Formate at Indium Electrodes with High Efficiency and Selectivity in pH Neutral Electrolytes, Appl. Catal. B: Environ. 238 (2018) 546–556. [7] D. Du, R. Lan, J. Humphreys, S. Tao, Progress in Inorganic Cathode Catalysts for Electrochemical Conversion of Carbon Dioxide into Formate or Formic acid, J. Appl. Electrochem. 47 (2017) 661–678. [8] X. Zhang, X.F. Hou, Q. Zhang, Y.X. Cai, Y.Y. Liu, J.L. Qiao, Polyethylene Glycol Induced Reconstructing Bi Nanoparticle Size for Stabilized CO2Electroreduction to Formate, J. Catal. 365 (2018) 63–70. [9] X. Zhang, T. Lei, Y.Y. Liu, J.L. Qiao, Enhancing CO2Electrolysis to Formate on
[19]
[20]
[21]
[22]
[23] [24]
[25]
[26]
[27]
358
Facilely Synthesized Bi Catalysts at Low Overpotential, Appl. Catal. B: Environ. 218 (2017) 46–50. H. Yang, N. Han, J. Deng, J.H. Wu, Y. Wang, Y.P. Hu, P. Ding, Y.F. Li, Y.G. Li, J. Lu, Selective CO2Reduction on 2D Mesoporous Bi Nanosheets, Adv. Energy Mater. 8 (2018) 1801536. S. Kim, W.J. Dong, S. Gim, W. Sohn, J.Y. Park, C.J. Yoo, H.W. Jang, J.L. Lee, Shapecontrolled Bismuth Banoflakes as Highly Selective Catalysts for Electrochemical Carbon Dioxide Reduction to Formate, Nano Energy 39 (2017) 44–52. Y. Wang, M.M. Shi, D. Bao, F.L. Meng, Q. Zhang, Y.T. Zhou, K.H. Liu, Y. Zhang, J.Z. Wang, Z.W. Chen, D.P. Liu, Z. Jiang, M. Luo, L. Gu, Q.H. Zhang, X.Z. Cao, Y. Yao, M.H. Shao, Y. Zhang, X.B. Zhang, J.G.G. Chen, J.M. Yan, Q. Jiang, Generating Defect-Rich Bismuth for Enhancing the Rate of Nitrogen Electroreduction to Ammonia, Angew. Chem. Int. Edit. 58 (2019) 9464–9469. Y. Zhang, F.W. Li, X.L. Zhang, T. Williams, C.D. Easton, A.M. Bond, J. Zhang, Electrochemical Reduction of CO2 on Defect-rich Bi Derived from Bi2S3with Enhanced Formate Selectivity, J. Mater. Chem. A 6 (2018) 4714–4720. X.L. Zhang, X.H. Sun, S.X. Guo, A.M. Bond, J. Zhang, Formation of Lattice-dislocated Bismuth Nanowires on Copper Foam for Enhanced Electrocatalytic CO2 Reduction at Low Overpotential, Energy Environ. Sci. 12 (2019) 1334–1340. Q.F. Gong, P. Ding, M.Q. Xu, X.R. Zhu, M.Y. Wang, J. Deng, Q. Ma, N. Han, Y. Zhu, J. Lu, Z.X. Feng, Y.F. Li, W. Zhou, Y.G. Li, Structural Defects on Converted Bismuth Oxide Nanotubes Enable Highly Active Electrocatalysis of Carbon Dioxide Reduction, Nat. Commun. 10 (2019) 2807. C.W. Lee, J.S. Hong, K.D. Yang, K. Jin, J.H. Lee, H.Y. Ahn, H. Seo, N.E. Sung, K.T. Nam, Selective Electrochemical Production of Formate from Carbon Dioxide with Bismuth-Based Catalysts in an Aqueous Electrolyte, ACS Catal. 8 (2018) 931–937. Z.R. Zhang, F. Ahmad, W.H. Zhao, W.S. Yan, W.H. Zhang, H.W. Huang, C. Ma, J. Zeng, Enhanced Electrocatalytic Reduction of CO2 via Chemical Coupling between Indium Oxide and Reduced Graphene Oxide, Nano Lett. 19 (2019) 4029–4034. J.W. Liu, Q.L. Ma, Z.Q. Huang, G.G. Liu, H. Zhang, Recent Progress in GrapheneBased Noble-Metal Nanocomposites for Electrocatalytic Applications, Adv. Mater. 31 (2019) 1800696. Z. Li, Y.R. Cui, Z.W. Wu, C. Milligan, L. Zhou, G. Mitchell, B. Xu, E.Z. Shi, J.T. Miller, F.H. Ribeiro, Y. Wu, Reactive metal-support interactions at moderate temperature in two-dimensional niobium-carbide-supported platinum catalysts, Nat. Catal. 1 (2018) 349–355. Y. Suchorski, S.M. Kozlov, I. Bespalov, M. Datler, D. Vogel, Z. Budinska, K.M. Neyman, G. Rupprechter, The Role of Metal/oxide Interfaces for Long-range Metal Particle Activation During CO Oxidation, Nat. Mater. 17 (2018) 519. N.J. O’Connor, A.S.M. Jonayat, M.J. Janik, T.P. Senftle, Interaction trends between single metal atoms and oxide supports identified with density functional theory and statistical learning, Nat. Catal. 1 (2018) 531–539. S. Navalon, A. Dhakshinamoorthy, M. Alvaro, H. Garciaa, Metal Nanoparticles Supported on Two-dimensional Graphenes as Heterogeneous Catalysts, Coordin. Chem. Rev. 312 (2016) 99–148. G. Pacchioni, H.J. Freund, Controlling the charge state of supported nanoparticles in catalysis: lessons from model systems, Chem. Soc. Rev. 47 (2018) 8474–8502. L.Y. Lin, Y. Nie, S. Kavadiya, T. Soundappan, P. Biswas, N-doped Reduced Graphene Oxide Promoted Nano TiO2as a Bifunctional Adsorbent/photocatalyst for CO2 Photoreduction: Effect of N species, Chem. Eng. J. 316 (2017) 449–460. X.Y. Cui, S.B. Yang, X.X. Yan, J.G. Leng, S. Shuang, P.M. Ajayan, Z.J. Zhang, Pyridinic-Nitrogen-Dominated Graphene Aerogels with Fe-N-C Coordination for Highly Efficient Oxygen Reduction Reaction, Adv. Funct. Mater. 26 (2016) 5708–5717. T.W. van Deelen, C. Hernández Mejía, K.P. de Jong, Control of metal-support interactions in heterogeneous catalysts to enhance activity and selectivity, Nat. Catal. (2019) 1–16. W.J. Zhang, Y. Hu, L.B. Ma, G.Y. Zhu, P.Y. Zhao, X.L. Xue, R.P. Chen, S.Y. Yang,
Journal of CO₂ Utilization 37 (2020) 353–359
D. Wu, et al.
electrochemical CO2 reduction, J. CO₂ Util. 30 (2019) 168–182. [30] Z. Chen, K. Mou, X. Wang, L. Liu, Nitrogen-Doped Graphene Quantum Dots Enhance the Activity of Bi2O3Nanosheets for Electrochemical Reduction of CO2 in a Wide Negative Potential Region, Angew. Chem. Int. Edit. 130 (2018) 12792–12796. [31] L.C. Liu, A. Corma, Metal catalysts for heterogeneous catalysis: from single atoms to nanoclusters and nanoparticles, Chem. Rev. 118 (2018) 4981–5079.
J. Ma, J. Liu, Z. Jin, Liquid-phase Exfoliated Ultrathin Bi Nanosheets: Uncovering the Origins of Enhanced Electrocatalytic CO2 Reduction on Two-dimensional Metal Nanostructure, Nano Energy 53 (2018) 808–816. [28] M. Dunwell, W. Luc, Y.S. Yan, F. Jiao, B.J. Xu. Understanding surface-mediated electrochemical reactions: CO2 reduction and beyond, ACS Catal. 8 (2018) 8121–8129. [29] T. Ma, Q. Fan, X. Li, J. Qiu, T. Wu, Z. Sun, Graphene-based materials for
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Metal-support interaction enhanced electrochemical reduction of CO2 to formate between graphene and Bi nanoparticles
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Dan Wua, Wenyue Chena, Xuewan Wanga, Xian-Zhu Fua,*, Jing-Li Luoa,b,** a b
College of Materials Science and Engineering, Shenzhen University, 1066 Xueyuan Ave., Shenzhen, China Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, T6G 1H9, Canada
A R T I C LE I N FO
A B S T R A C T
Keywords: Metal-Support interaction Bismuth CO2electroreduction Graphene Formate
Metal nanoparticles stabilized on a support material have been explored extensively to boost heterogeneous catalysis. Herein, the effect of metal-support interaction between bismuth (Bi) nanoparticles and reduced graphene oxide nanosheets (Gr) on the electroreduction of CO2 towards value-added formate is explored. The obtained Bi/Gr hybrid catalysts exhibit a superior catalytic activity towards electrochemical reduction of CO2, which gives the maximum faradic efficiency of 92.1 % at -0.97 V (vs. RHE) for formate generation. Particularly, the hydride shows an enhancement to the catalysts of bare Bi and physical mixture of Bi and Gr, with a high current density of 28.1 mA∙cm−2 and production rate of 0.53 mol∙cm−2 h-1 at -1.17 V (vs. RHE) for formate generation. The electrochemical analysis reveals that the metal-support interactions substantially boost CO2 electroreduction activity through modification the electronic structure and improving interfacial electron transfer between Bi and Gr. This work not only deepens an understanding of metal-support interaction effect but also sheds light on the design of high-efficiency catalysts toward CO2 electroreduction by virtue of the interactions between active metals and carbon-like support.
1. Introduction The worldwide overproduction of carbon dioxide (CO2) brings about serious environmental pollution and climate change issues. In this regard, electrocatalytic conversion of CO2 to value-added chemicals is regarded as a prospective pathway for simultaneous recycling of carbon resource and the generation of energy-rich fuels [1,2]. Among various CO2 reduction chemicals, formic acid (FA) is a promising nonflammable energy-storage liquid media and a natural biomass for the sustainable development of human civilization [3,4]. Taking the advantage of two-electron reduction process, less energy input is required to overcome the kinetic barriers for FA generation compared to the higher order CO2 reduction products which needs activating multielectron transfers. To this end, numerous improvements are devoted to various electrocatalysts to simultaneously achieve desirable catalytic activity and FA selectivity. Substantial experimental and theoretical efforts have been documented that certain metal electrocatalysts, such as Pd, Sn, Pb, Bi, In and Cd, can selectively make FA from CO2 [5–7]. Owing to the merits of cost-effectiveness and eco-friendliness, metallic Bi has been considered as a promising candidate for electrochemical conversion of CO2 to FA
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compared to noble and toxic metals. Currently, the electrocatalytic activity and FA selectivity of Bi is regulated by different features, including particle size [8,9], morphology [4,10,11], defect [12–15], and so forth. Beyond these intrinsic characteristics, immobilizing Bi nanoparticles on the support matrix to improve the stability and control the spatial distribution is one of the critical strategies. The so-called strong interaction between metal and substrate (metal-support interaction) also offer great opportunities for the improvements of electrocatalytic performance [16–18]. However, the metal-support interactions can also give rise to new interfacial phenomena. Therefore, controlling this interaction to optimize the electrocatalytic activity are highly desired. Generally, various types of catalyst support have been developed to immobilize metal nanoparticles, such as carbon materials, oxides and nitrides [19–21]. Particularly, graphene, a typical two-dimensional carbon material, is considered as an ideal platform for metal catalysts, which is featured with large surface area, high conductivity and good stability [18]. In this regard, immobilizing metal nanoparticles on graphene support prohibits the aggregation of particles by controlling their spatial distribution. Moreover, the graphene nanosheets supported open structure enables fully exposed active sites to adsorb and activate CO2 molecules, thus further contributing to enhanced overall
Corresponding author. Corresponding author at: College of Materials Science and Engineering, Shenzhen University, 1066 Xueyuan Ave., Shenzhen, China. E-mail addresses: [email protected] (X.-Z. Fu), [email protected] (J.-L. Luo).
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https://doi.org/10.1016/j.jcou.2020.02.007 Received 27 November 2019; Received in revised form 8 February 2020; Accepted 10 February 2020 2212-9820/ © 2020 Elsevier Ltd. All rights reserved.
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electroactivity and durability [22]. More importantly, the interface between metal nanoparticles and the support can give rise to a redistribution of electrons with noticeable effects [23]. In general, electron transfer is observed once metal nanoparticles contact with the support to facilitate the charge transfer and further improve the catalytic activity. As a result, coupling Bi nanoparticles with graphene nanosheet support is expected to bring many possibilities to improve the catalytic activity and stability in the electrochemical CO2 reduction process. In this work, Bi nanoparticles are uniformly deposited on reduced graphene oxide nanosheets (Gr) via a simple hydrothermal method. The metal-support interaction between Bi nanoparticles and Gr nanosheet substrate is confirmed. The influence of metal-support interaction on the catalytic activity and FA selectivity for electroreduction of CO2 on Bi/Gr hybrid is fully explored. Such interaction induced enhancement is revealed by experimental results and electrochemical analysis. 2. Experimental section
Fig. 1. XRD patterns of Bi/Gr and pure Bi samples.
2.1. Synthesis of Bi/Gr
separately purged into anodic and cathodic counterparts under mild stirring at 500 rpm throughout the experiments. During the electrolysis, CO2 delivered to the cathodic counterpart was routed into gas chromatography (GC, Fili, 9790Plus) equipped with a TCD detector and an FID detector to monitor the gas products. The KHCO3 solution after electrolysis was collected and analyzed on an ion chromatograph (IC, Shenghan, CIC-D120) to quantify liquid products.
Graphene oxide (GO) was prepared by using a modified Hummers method as described in Supporting Information. In a typical synthesis of Bi/Gr, 10 mg Bi(NO3)3 was added to 10 mL of GO (1 mg mL−1) with further ultrasonication for 20 min to form a uniform suspension. Subsequently, 5 mL of hydrazine hydrate (85 wt%) was added into the suspension and the solution pH was adjusted to 11 using aqua ammonia (28 wt%). After stirring for 30 min, the mixture was transferred into a Teflon-sealed autoclave at 120 °C for 18 h and then naturally cooled down to room temperature. After washing with DI water and ethanol several times, the product was freeze-dried for 24 h and the product was denoted as Bi/Gr. For comparison, a series of samples was also prepared by the same procedure expect for different addition amount of Bi(NO3)3 precursor. The obtained catalysts were denoted as 0.1Bi/Gr, 0.5Bi/Gr and 3Bi/Gr, respectively, when the mass ratio of Bi(NO3)3/GO precursor was 0.1, 0.5 and 3. The pure Bi nanoparticles and Gr nanosheets were also prepared through the similar procedure respectively in the absence of GO and Bi(NO3)3. The physical mixture of Bi nanoparticles and Gr nanosheets (Bi-Gr) was also obtained for comparison.
3. Results and discussion Fig. 1 shows the XRD patterns of the obtained samples. All the diffraction peaks of Bi/Gr can be assigned to the rhombohedral phase of Bi (PDF 00-044-1246). No observable peaks related to bismuth oxide are found, evidencing high phase-purity of Bi/Gr. Moreover, no discernible the diffraction peaks of Gr can be observed, probably due to the relatively low diffraction intensity of Gr in the hybrid. Noticeably, the insert shows a clear peak shift of Bi/Gr compared to the pure Bi, suggesting the alteration of interlayer spacing of layer Bi crystal structure induced by a strong interaction between Gr support and Bi particles. GO with negatively charged oxygen-containing functional groups can facilitate the coordination with positively charged Bi3+ ions. A further hydrothermal treatment results in a further simultaneous reduction of GO and Bi3+ ions. Furthermore, the hydrazine-involved redox can yield N2 gas, which can create an inert atmosphere and thus prevent the Bi NPs from re-oxidation in the aqueous solution, resulting in the formation of Bi/Gr hybrids. According to the ICP-OES measurement, the Bi loading in Bi/Gr hybrid is determined to be 41.2 wt%. The chemical coupling also can also greatly affect the surface chemistry of materials. XPS spectra were carried out to probe the elemental chemical state. The high-resolution of C 1s spectra in Fig. 2a can be deconvoluted into a dominated peak for CeC/C = C/C–H bond at 284.7 eV, along with weak peaks of C]N bond at 285.6 eV, CeO/C-N bond at 286.9 eV, C]O bond at 288.4 eV and HOeC = O bond at 290.7 eV, respectively. The dominated sp2-bonded carbon atoms suggest a high carbonization degree of Bi/Gr and an excellent conductivity for the catalysts could be expected. The N 1s XPS spectra (Fig. 2b) of Bi/ Gr is fitted into three typical peaks corresponding to the graphitic N (401.9 eV), the pyrrolic N (399.8 eV) and the pyridinic N (ca. 398.3 eV). Besides the decreased overall N content, the graphitic N content in Bi/ Gr catalysts increases while the pyridinic N content is reduced at relatively low levels compared to the Gr sample (Table S1). This is because the introduction of Bi heteroatoms disrupts the configurations of bulk Gr nanosheets, resulting in a decreased graphitic N and more edges available for the formation of pyridinic N [24,25]. Moreover, the pyrrolic N is the primary N bonding state in Bi/Gr and Gr catalysts whereas the binding energy of graphitic N and pyridinic N in Bi/Gr shift in comparison with that of Gr, which is ascribed to the changes of N-
2.2. Characterizations The X-ray diffraction (XRD) pattern were recorded on a SmartLab (Rigaku) diffractometer. The morphology of samples was obtained on a high-resolution transmission scanning electron microscope (HRTEM, JEM-F200). The Raman spectra were recorded using a Raman microscope (LabRam HR, Horiba evolution). The XPS data were obtained from a K-Alpha X-ray photoelectron spectrometer (Thermo Scientific). The mass loading of Bi in the hybrid was determined by an inductively coupled plasma optical emission spectrometer (ICP-OES, Perkin Elmer Optima 2100 DV). 2.3. Electrochemical measurements The electrochemical measurements were conducted using a H-type reactor on a three-electrode system using Pt foil as the counter electrode and Ag/AgCl as the reference electrode. Typically, 5 mg of Bi/Gr catalysts was added to a mixture of 950 μL ethanol and 50 μL Nafion solution (5 wt%), and sonicated for 1 h to form a homogeneous catalyst ink. Then, the catalyst ink was uniformly air-brushed onto a 1 × 1 cm2 carbon paper with a mass loading of 1 mg∙cm−2 to act as the working electrode. All potentials measured against Ag/AgCl electrode were converted to the RHE scale using equation of ERHE= EAg/AgCl + 0.197 V + 0.0591 × pH. The electrochemical reduction of CO2 was carried out in CO2-saturated 0.5 M KHCO3 electrolyte (pH = 7.3) at room temperature. Highpure CO2 at a flow rate of 20 mL min−1 was continuously and 354
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Fig. 2. High-resolution XPS spectra of (a) C 1s, (b) N 1s, (c) Bi 4f and (d) Raman spectra of samples.
interplanar spacing of 0.32 nm correspond to the (012) planes of rhombohedral Bi phase (Figs. 3b and S2), which is the low-energy facet of Bi [11]. This suggests that contact with the support can prevent the agglomeration and growth of Bi nanoparticles and lower the surface energy of Bi nanoparticles planes, favoring sphere shapes over others [26]. The EDX spectra (Fig. 3c) also verifies the homogenously immobilization of Bi on the Gr support matrix. The electrochemical activity of CO2 reduction on Bi/Gr catalyst is evaluated in a three-electrode system using a proton membrane separated H-type reactor. The LSV curves of Gr/Bi in Ar or CO2 saturated 0.5 M KHCO3 electrolyte are shown in Fig. 4a. Obviously, Bi/Gr catalysts exhibit significantly higher current density (j) in the CO2 saturated electrolyte than that in the Ar purged one at the same potential, indicating that Bi/Gr can effectively promote CO2 reduction and conversion with unfavorable hydrogen evolution reaction. Fig. 4b reports the faradaic efficiencies (FEs) as a function of cathodic potentials. For Bi/Gr catalysts, the liquid HCOOH is found as the major reduction product with minor gaseous H2 and negligible CO for CO2 electroreduction. The HCOOH is initially detected at -0.57 V (vs. RHE). The FE for HCOOH (FEHCOOH) rapidly increases and achieves the maximum value of 92.1 % at -0.97 V (vs. RHE). The FEHCOOH is further compared between bare Bi and Gr (Fig. 4c). No detectable HCOOH is found for Gr, suggesting that Bi is the active phase toward HCOOH generation in CO2 electroreduction. The FEHCOOH on Bi-Gr (the physical mixture of Bi nanoparticles and Gr nanosheets) is much lower than Bi/Gr at identical operating potentials. The highest FE is 83.2 % at -0.97 V (vs. RHE) with a sharp drop at more negative potentials. And similar spectral profile with slightly decreased FEHCOOH is observed for bare Bi sample. The
bonding configurations for two samples. As shown in Fig. 2c, the binding energies centered at 158.2 eV and 163.5 eV corresponds to Bi° and the shoulders situated at higher binding energies of 159.3 eV and 164.8 eV are assigned to Bi3+ in Bi/Gr composites. Comparatively, the bare Bi nanoparticles without support also have two doublets peaks related to Bi3+ and metallic Bi, but with different spectral profiles. The oxidized species are probably resulted from the surface oxidation of Bi nanoparticles during the characterizations. The above results evidence that the electronic structure of Bi and Gr in the hybrid is changed through the strong mutual interaction. The interface between a metal nanoparticle and the support matrix can give rise to a rearrangement of electrons within both materials [23,26]. Further surface information about the catalyst can be also obtained from Raman spectroscopy (Fig. 2d). For Bi/Gr catalysts, the peaks located at 64.5 and 89.9 cm−1 are referred to the characteristic Eg mode and A1g mode peaks of metallic Bi [4,27], while the doublet peaks at about 1330 and 1600 cm−1 are respectively accounted for the typical D and G bands. These peaks in the hybrids slightly shift compared with its bare counterparts, resulting from the metal-support interaction effect. Additionally, a weak peak at around 180 cm−1 attributing to the surface oxidation is found for both Bi and Bi/Gr samples, which is corresponded to the XPS results. The ultrathin nanosheet characteristic endows GO as perfect support substrate to disperse Bi ions (Fig. S1). The morphology of the representative Bi/Gr catalysts is characterized. The TEM image (Fig. 3a) shows that small Bi nanoparticles are uniformly dispersed on the Gr nanosheets without observable aggregation. The average size of the Bi nanoparticle is about 5 nm. A closer observation in Fig. 3b clearly exhibits the lattice fringes of Bi and Gr. The lattice fringes of an 355
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Fig. 3. (a) TEM, (b) HRTEM images and (c) EDX mappings of Bi/Gr sample.
Fig. 4. (a) LSV curves for Bi/Gr in Ar and CO2 saturated 0.5 M KHCO3, (b) FEs for Bi/Gr catalysts, (c) HCOOH faradic efficiencies (FEHCOOH) for Gr, Bi, Bi-Gr and Bi/ Gr catalysts, and (d) long-term satiability test at -0.87 V (vs. RHE) for 30 h on Bi/Gr catalysts. 356
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Fig. 5. (a) Partial current density and production rate for HCOOH production and (b) corresponding Tafel slops for Bi, Bi-Gr and Bi/Gr catalysts.
jHCOOH goes up first and then declines with the Bi3+/GO mass ratio rising from 0.1–3. Overall, the Bi/Gr catalysts show the best electrocatalytic CO2 reduction activity in terms of HCOOH selectivity and current density. This phenomenon is related to the morphological change of Bi nanoparticles in the hybrid. As demonstrated in Fig. S4, highly dispersed Bi nanoparticles in the 0.1Bi/Gr and 0.5Bi/Gr hybrid are less than 1 nm in size while aggregation and large bulk of Bi nanoparticles can be observed in the 3Bi/Gr hybrid. Since the Bi is the active phase towards HCOOH generation in CO2 electroreduction, less Bi addition or aggregation of Bi nanoparticles would reduce the active sites. Moreover, the generated reduction products of CO and H2 probably cover on the surface of ultra-small Bi nanoparticles, which is unfavorable for its interaction with CO2 molecules in the electrochemical CO2 conversion process. More importantly, A synergy can be created at the interface for the combination of Bi and Gr, which thus accelerates CO2 adsorption, intermediate binding and stability, benefiting CO2 to HCOOH conversion [29,30]. However, the metal-support interaction effect is attenuated for larger Bi nanoparticles because of the reduced impact of charge transfer and relatively reduced metallic surface area in intimate contact with the support [31]. Therefore, Bi/Gr hybrid with Bi nanoparticles in appropriate size is expected to exhibit the best electrocatalytic performance for CO2 reduction.
above results indicate that the strong interaction between Bi and Gr can enhance the HCOOH selectivity in electrochemical CO2 reduction. The long-term durability test of Bi/Gr illustrated in Fig. 4d shows negligible decays of the current density at -0.87 V (vs. RHE) over 30 h, manifesting a remarkable stability of Bi/Gr electrocatalysts. The in-depth understanding for the contribution of the metal-support interaction to the enhancement of electrochemical CO2 reduction activity is disclosed. The partial current density for HCOOH generation (jHCOOH) and HCOOH production rate on bare Bi, Bi-Gr and Bi/Gr catalysts are plotted in Fig. 5a. Overall, the Bi/Gr exhibits a much higher jHCOOH across potentials from -0.57 V (vs. RHE) to -1.17 V (vs. RHE). In contrast, the bare Bi and Bi-Gr catalysts show much lower jHCOOH with similar trend in CO2RR. More specifically, Bi/Gr reaches a maximum jHCOOH value of -28.1 mA∙cm−2 at -1.17 V (vs. RHE), which is higher than a maximum jHCOOH value of 7.9 and 14.1 mA∙cm−2 for Bi and Bi-Gr at the same cathodic potential. Simultaneously, the higher production rate is also expected for Bi/Gr catalysts. As evidenced in Fig. 5a, the HCOOH generation rate rapidly increases with more negative potentials to achieve 0.53 mol∙cm−2 h-1 at -1.17 V (vs. RHE), which is higher than that of Bi-Gr with a value of 0.26 mol∙cm−2 h-1 at -1.17 V (vs. RHE). The bare Bi gives a maximum value of 0.16 mol∙cm−2 h-1 at -1.07 V with subsequent decline at -1.17 V (vs. RHE). The results demonstrate that the metal-support interaction can facilitate the surface charge transfer between Bi and Gr, favoring for the CO2 reduction. Tafel analysis offer valuable insights into reaction mechanisms. As calculated in Fig. 5b, the Tafel slops of Bi, Bi-Gr and Bi/Gr catalysts are 185, 167 and 152 mV dec-1, respectively. These values are close to the theoretical value of 118 mV dec-1, suggesting the initial electron transfer or proton-coupled electron transfer is the rate limiting step in CO2 electroreduction process [28]. The smallest Tafel slop of Bi/Gr implies its fastest reaction kinetics. Based on the above analysis, Bi/Gr with two-dimensional nanostructure offer more active site for CO2 adsorption and the strong interaction can improve interfacial charge-transfer, which is advantageous for the subsequent CO2 activation and conversion to HCOOH, resulting in enhanced electrochemical activity in CO2RR. The influence of the Bi nanoparticle loading mass in the hybrid on the HCOOH generation is also investigated. The Bi amount in the 0.1Bi/ Gr, 0.5 Bi/Gr and 3Bi/Gr hybrid is measured to be 4.6 wt.%, 20.9 w.t.% and 93.6 wt.%, respectively. As shown in Fig. 6a, the overall FEHCOOH of hybrid increases across the tested negative potentials ranging from -0.57 V (vs. RHE) to -1.17 V (vs. RHE) when the Bi loading amount increases in succession from 0.1Bi/Gr, 0.5 Bi/Gr to Bi/Gr catalysts. However, when further increasing the Bi loading, the overall FEHCOOH of 3Bi/Gr catalysts drops. The profiles of total current density for these catalysts are plotted in Fig. S3. Accordingly, the partial current density for HCOOH generation (jHCOOH) is calculated. The evolution of jHCOOH with different loading of Bi follows similar trend (Fig. 6b). The value of
4. Conclusions Bi/Gr hybrids are synthesized with the construction of metal-support interaction between Bi nanoparticles and ultrathin Gr nanosheets. This interaction can considerably improve the electrochemical performance of CO2 reduction, resulting in high faradic efficiency over a wide negative potential range. In specific, Bi/Gr gives a current density of 28.1 mA∙cm−2 and production rate of 0.53 mol∙cm−2 h-1 at -1.17 V (vs. RHE) for formate generation, which is about 2 times higher than those of physically mixed Bi-Gr samples. The precursor Bi3+/GO ratio also affects the faradaic efficiency and current density for formate production. The kinetically experimental evidence reveals that the strong metal-support interaction mainly attributes to the enhanced electrochemical CO2 reduction activity by improving the interfacial electron transfer ability. We believe the present work provides a promising alternative strategy for metallic Bi to maximize the catalytic activity toward electroreduction of CO2 into value-added formate. CRediT authorship contribution statement Dan Wu: Conceptualization, Methodology, Validation, Formal analysis, Writing - original draft, Project administration. Wenyue Chen: Investigation. Xuewan Wang: Resources, Funding acquisition. Xian-Zhu Fu: Resources, Writing - review & editing, Visualization, 357
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Fig. 6. (a) FEHCOOH and (b) jHCOOH of 0.1Bi/Gr, 0/5Bi/Gr, Bi/Gr and 3Bi/Gr catalysts.
Funding acquisition. Jing-Li Luo: Resources, Supervision. [10]
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
[11]
[12]
Acknowledgements This work was financially supported by the National Natural Science Foundation of China (No. 21975163and51902204) and Bureau of Industry and Information Technology of Shenzhen (No. 201901171518). The authors would like to acknowledge the technical support provided by Instrumental Analysis Center of Shenzhen University (Xili Campus) and thank Yang Chengyu from Shiyanjia Lab (www.shiyanjia.com) for the XPS experiments.
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Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.jcou.2020.02.007.
[17]
References
[18]
[1] W.J. Zhang, Y. Hu, L.B. Ma, G.Y. Zhu, Y.R. Wang, X.L. Xue, R.P. Chen, S.Y. Yang, Z. Jin, Progress and Perspective of Electrocatalytic CO2 Reduction for Renewable Carbonaceous Fuels and Chemicals, Adv. Sci. 5 (2018) 1700275. [2] M.G. Kibria, J.P. Edwards, C.M. Gabardo, C.T. Dinh, A. Seifitokaldani, D. Sinton, E.H. Sargent, Electrochemical CO2Reduction into Chemical Feedstocks: From Mechanistic Electrocatalysis Models to System Design, Adv. Mater. 31 (2019) 1807166. [3] B. Jiang, X.G. Zhang, K. Jiang, D.Y. Wu, W.B. Cai, Boosting Formate Production in Electrocatalytic CO2 Reduction over Wide Potential Window on Pd Surfaces, J. Am. Chem. Soc. 140 (2018) 2880–2889. [4] D. Wu, J.W. Liu, Y. Liang, K. Xiang, X.Z. Fu, J.L. Luo, Electrochemical Transformation of Facet-Controlled BiOI into Mesoporous Bismuth Nanosheets for Selective Electrocatalytic Reduction of CO2 to Formic Acid, ChemSusChem 12 (2019) 4700–4707. [5] J.E. Pander, M.F. Baruch, A.B. Bocarsly, Probing the Mechanism of Aqueous CO2Reduction on Post-Transition-Metal Electrodes using ATR-IR Spectroelectrochemistry, ACS Catal. 6 (2016) 7824–7833. [6] R. Hegner, L.F.M. Rosa, F. Harnisch, Electrochemical CO2Reduction to Formate at Indium Electrodes with High Efficiency and Selectivity in pH Neutral Electrolytes, Appl. Catal. B: Environ. 238 (2018) 546–556. [7] D. Du, R. Lan, J. Humphreys, S. Tao, Progress in Inorganic Cathode Catalysts for Electrochemical Conversion of Carbon Dioxide into Formate or Formic acid, J. Appl. Electrochem. 47 (2017) 661–678. [8] X. Zhang, X.F. Hou, Q. Zhang, Y.X. Cai, Y.Y. Liu, J.L. Qiao, Polyethylene Glycol Induced Reconstructing Bi Nanoparticle Size for Stabilized CO2Electroreduction to Formate, J. Catal. 365 (2018) 63–70. [9] X. Zhang, T. Lei, Y.Y. Liu, J.L. Qiao, Enhancing CO2Electrolysis to Formate on
[19]
[20]
[21]
[22]
[23] [24]
[25]
[26]
[27]
358
Facilely Synthesized Bi Catalysts at Low Overpotential, Appl. Catal. B: Environ. 218 (2017) 46–50. H. Yang, N. Han, J. Deng, J.H. Wu, Y. Wang, Y.P. Hu, P. Ding, Y.F. Li, Y.G. Li, J. Lu, Selective CO2Reduction on 2D Mesoporous Bi Nanosheets, Adv. Energy Mater. 8 (2018) 1801536. S. Kim, W.J. Dong, S. Gim, W. Sohn, J.Y. Park, C.J. Yoo, H.W. Jang, J.L. Lee, Shapecontrolled Bismuth Banoflakes as Highly Selective Catalysts for Electrochemical Carbon Dioxide Reduction to Formate, Nano Energy 39 (2017) 44–52. Y. Wang, M.M. Shi, D. Bao, F.L. Meng, Q. Zhang, Y.T. Zhou, K.H. Liu, Y. Zhang, J.Z. Wang, Z.W. Chen, D.P. Liu, Z. Jiang, M. Luo, L. Gu, Q.H. Zhang, X.Z. Cao, Y. Yao, M.H. Shao, Y. Zhang, X.B. Zhang, J.G.G. Chen, J.M. Yan, Q. Jiang, Generating Defect-Rich Bismuth for Enhancing the Rate of Nitrogen Electroreduction to Ammonia, Angew. Chem. Int. Edit. 58 (2019) 9464–9469. Y. Zhang, F.W. Li, X.L. Zhang, T. Williams, C.D. Easton, A.M. Bond, J. Zhang, Electrochemical Reduction of CO2 on Defect-rich Bi Derived from Bi2S3with Enhanced Formate Selectivity, J. Mater. Chem. A 6 (2018) 4714–4720. X.L. Zhang, X.H. Sun, S.X. Guo, A.M. Bond, J. Zhang, Formation of Lattice-dislocated Bismuth Nanowires on Copper Foam for Enhanced Electrocatalytic CO2 Reduction at Low Overpotential, Energy Environ. Sci. 12 (2019) 1334–1340. Q.F. Gong, P. Ding, M.Q. Xu, X.R. Zhu, M.Y. Wang, J. Deng, Q. Ma, N. Han, Y. Zhu, J. Lu, Z.X. Feng, Y.F. Li, W. Zhou, Y.G. Li, Structural Defects on Converted Bismuth Oxide Nanotubes Enable Highly Active Electrocatalysis of Carbon Dioxide Reduction, Nat. Commun. 10 (2019) 2807. C.W. Lee, J.S. Hong, K.D. Yang, K. Jin, J.H. Lee, H.Y. Ahn, H. Seo, N.E. Sung, K.T. Nam, Selective Electrochemical Production of Formate from Carbon Dioxide with Bismuth-Based Catalysts in an Aqueous Electrolyte, ACS Catal. 8 (2018) 931–937. Z.R. Zhang, F. Ahmad, W.H. Zhao, W.S. Yan, W.H. Zhang, H.W. Huang, C. Ma, J. Zeng, Enhanced Electrocatalytic Reduction of CO2 via Chemical Coupling between Indium Oxide and Reduced Graphene Oxide, Nano Lett. 19 (2019) 4029–4034. J.W. Liu, Q.L. Ma, Z.Q. Huang, G.G. Liu, H. Zhang, Recent Progress in GrapheneBased Noble-Metal Nanocomposites for Electrocatalytic Applications, Adv. Mater. 31 (2019) 1800696. Z. Li, Y.R. Cui, Z.W. Wu, C. Milligan, L. Zhou, G. Mitchell, B. Xu, E.Z. Shi, J.T. Miller, F.H. Ribeiro, Y. Wu, Reactive metal-support interactions at moderate temperature in two-dimensional niobium-carbide-supported platinum catalysts, Nat. Catal. 1 (2018) 349–355. Y. Suchorski, S.M. Kozlov, I. Bespalov, M. Datler, D. Vogel, Z. Budinska, K.M. Neyman, G. Rupprechter, The Role of Metal/oxide Interfaces for Long-range Metal Particle Activation During CO Oxidation, Nat. Mater. 17 (2018) 519. N.J. O’Connor, A.S.M. Jonayat, M.J. Janik, T.P. Senftle, Interaction trends between single metal atoms and oxide supports identified with density functional theory and statistical learning, Nat. Catal. 1 (2018) 531–539. S. Navalon, A. Dhakshinamoorthy, M. Alvaro, H. Garciaa, Metal Nanoparticles Supported on Two-dimensional Graphenes as Heterogeneous Catalysts, Coordin. Chem. Rev. 312 (2016) 99–148. G. Pacchioni, H.J. Freund, Controlling the charge state of supported nanoparticles in catalysis: lessons from model systems, Chem. Soc. Rev. 47 (2018) 8474–8502. L.Y. Lin, Y. Nie, S. Kavadiya, T. Soundappan, P. Biswas, N-doped Reduced Graphene Oxide Promoted Nano TiO2as a Bifunctional Adsorbent/photocatalyst for CO2 Photoreduction: Effect of N species, Chem. Eng. J. 316 (2017) 449–460. X.Y. Cui, S.B. Yang, X.X. Yan, J.G. Leng, S. Shuang, P.M. Ajayan, Z.J. Zhang, Pyridinic-Nitrogen-Dominated Graphene Aerogels with Fe-N-C Coordination for Highly Efficient Oxygen Reduction Reaction, Adv. Funct. Mater. 26 (2016) 5708–5717. T.W. van Deelen, C. Hernández Mejía, K.P. de Jong, Control of metal-support interactions in heterogeneous catalysts to enhance activity and selectivity, Nat. Catal. (2019) 1–16. W.J. Zhang, Y. Hu, L.B. Ma, G.Y. Zhu, P.Y. Zhao, X.L. Xue, R.P. Chen, S.Y. Yang,
Journal of CO₂ Utilization 37 (2020) 353–359
D. Wu, et al.
electrochemical CO2 reduction, J. CO₂ Util. 30 (2019) 168–182. [30] Z. Chen, K. Mou, X. Wang, L. Liu, Nitrogen-Doped Graphene Quantum Dots Enhance the Activity of Bi2O3Nanosheets for Electrochemical Reduction of CO2 in a Wide Negative Potential Region, Angew. Chem. Int. Edit. 130 (2018) 12792–12796. [31] L.C. Liu, A. Corma, Metal catalysts for heterogeneous catalysis: from single atoms to nanoclusters and nanoparticles, Chem. Rev. 118 (2018) 4981–5079.
J. Ma, J. Liu, Z. Jin, Liquid-phase Exfoliated Ultrathin Bi Nanosheets: Uncovering the Origins of Enhanced Electrocatalytic CO2 Reduction on Two-dimensional Metal Nanostructure, Nano Energy 53 (2018) 808–816. [28] M. Dunwell, W. Luc, Y.S. Yan, F. Jiao, B.J. Xu. Understanding surface-mediated electrochemical reactions: CO2 reduction and beyond, ACS Catal. 8 (2018) 8121–8129. [29] T. Ma, Q. Fan, X. Li, J. Qiu, T. Wu, Z. Sun, Graphene-based materials for
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