Mild and selective hydrogenation of CO2 into formic acid over electron-rich MoC nanocatalysts

Journal Pre-proofs Article Mild and selective hydrogenation of CO2 into formic acid over electron-rich MoC nanocatalysts Hong-Hui Wang, Shi-Nan Zhang, Tian-Jian Zhao, Yong-Xing Liu, Xi Liu, Juan Su, Xin-Hao Li, Jie-Sheng Chen PII: DOI: Reference:

S2095-9273(20)30065-7 https://doi.org/10.1016/j.scib.2020.02.004 SCIB 953

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Science Bulletin

Received Date: Revised Date: Accepted Date:

4 December 2019 8 January 2020 4 February 2020

Please cite this article as: H-H. Wang, S-N. Zhang, T-J. Zhao, Y-X. Liu, X. Liu, J. Su, X-H. Li, J-S. Chen, Mild and selective hydrogenation of CO2 into formic acid over electron-rich MoC nanocatalysts, Science Bulletin (2020), doi: https://doi.org/10.1016/j.scib.2020.02.004

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Mild and selective hydrogenation of CO2 into formic acid over electron-rich MoC nanocatalysts Hong-Hui Wang,1 Shi-Nan Zhang,1 Tian-Jian Zhao,1 Yong-Xing Liu,1 Xi Liu,1,2 Juan Su,1,3 Xin-Hao Li,1* and Jie-Sheng Chen1 1School

of Chemistry and Chemical Engineering, Shanghai Jiao Tong University,

Shanghai 200240, China. 2SynCat@Beijing, 3State

Synfuels China Technology Co., Ltd, Beijing 101407, China.

Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of

Chemistry, Jilin University, Changchun 130012, China. *Corresponding authors: [email protected], (X. H. L).

Received: 04-Dec-2019 Revised: 08-Jan-2020 Accepted: 4-Feb-2020

1

Abstract The direct hydrogenation of CO2 using H2 gas is a one-stone-two-birds route to produce highly value-added hydrocarbon compounds and to lower the CO2 level in the atmosphere. However, the transformation of CO2 and H2 into hydrocarbons has always been a great challenge while ensuring both the activity and selectivity over abundant-element-based nanocatalysts. In this work, we designed a Schottky heterojunction composed of electron-rich MoC nanoparticles embedded inside an optimized nitrogen-doped carbon support (MoC@NC) as the first example of noble-metal-free heterogeneous catalysts to boost the activity of and specific selectivity for CO2 hydrogenation to formic acid (FA) in liquid phase under mild conditions (2 MPa pressure and 70 °C). The MoC@NC catalyst with a high turnover frequency (TOF) of 8.20 molFA molMoC−1 h−1 at 140 °C and an excellent reusability are more favorable for real applications.

Key words: MoC • CO2 hydrogenation • Mott-Schottky effect • heterojunction • formic acid

1. Introduction: CO2 released to the atmosphere has reached an unprecedented level due to fossil-fuel use, thus, causing a negative influence on the global environment. Apart from reducing CO2 emissions, the cost-effective conversion of CO2 into highly value-added organic compounds [1-5] is an important strategy of CO2 fixation to address the related environmental issues. The heterogeneous hydrogenation of CO2 into hydrocarbons, including methane, methanol, formic acid (FA), ethanol, ethylene, aromatics, olefin and so on [6-14], using abundant element-based catalysts has thus been intensively investigated during the past decades. Among the products from CO2 reduction, FA has been recognized as an excellent candidate for liquid-phase hydrogen-energy carriers with low-toxicity and a high volumetric hydrogen density (53 g H2 LFA−1) [15-18]. In combination with the 2

unfavorable thermodynamics of the hydrogenation reaction of CO2 to FA (ΔG°298 = + 32.9 kJ mol−1), the diversity of possible products also requires critical conditions or to control the selectivity of the CO2 hydrogenation reaction towards FA over current catalysts, the majority of which are Pd-based or noble-metal-containing catalysts [19]. Apart from their high cost, the noble-metal-based catalysts also suffer from unwanted dehydrogenation of FA back to CO2, and even CO, and from their susceptibility to the poison effect of CO formed in situ. Besides using a fixed-bed reactor to avoid dehydrogenation of FA [20], boosting the activity of cheap transition-metal-based heterogeneous catalysts, including metal oxides [21], carbides [22] and nitrides [23-26], with presumably good chemical tolerance to FA poses the key challenge to hydrogenating CO2 on a massive scale. Herein, we described the design of an innovative dyad composed of inexpensive molybdenum carbide nanocrystals with nitrogen-doped carbon sheaths for activating CO2 and H2 molecules under very mild conditions. The rectifying contact between molybdenum carbide, as the metallic phase, and the nitrogen-doped carbon support, with an opened band gap, was applied to significantly enhance the electron enrichment of the supported molybdenum carbide nanoparticles. Theoretical simulations revealed, and then experimental results confirmed that such an electron-rich molybdenum carbide nanocatalyst with satisfied stability could tremendously decrease the activation energy of the hydrogenation reaction of CO2, giving a turnover frequency (TOF) value of 0.15 molFA molMoC−1 h−1 at 70 °C.

2. Materials and methods 2.1 Materials Melamine (99%, Aladdin), phosphomolybdic acid (PMo12, AR, Sinopharm), cyanoguanidine (DCDA, 99.5%, Acros), glucose (AR, Sinopharm), Ammonium heptamolybdate (99.9% metals basis, Aladdin), triethylamine (NEt3, ≥ 99.0%, Sinopharm), dimethylsulfoxide (DMSO, 99.8%, Aladdin), o-phenylendiamine (98%, GR, Acros), HCl (36%−38%, GR, Sinopharm), D2O (99 atom % D, Aladdin). All 3

chemicals were used without any further purification.

2.2 Synthesis of MoC@NxC Typically, 0.4 g melamine was dissolved in 200 mL deionized water, then, PMo12 solution (an equal amount of solute dissolved in 50 mL deionized water) was added to the above solution, leaving the mixture self-assembling until white solids formed. After that, remove water and blend the assembly uniformly with 32 g DCDA mechanically. Finally, the mixture was transferred to a covered crucible, and heated to 400 °C at a rate of 2 °C min−1, holding for 1h, then continued to 800 °C (or 900, 1000 °C) at 5 °C min−1, after holding for 4h, cooled down to room temperature naturally. The whole process of temperature programming was under the protection of N2. The obtained black fluffy solids were ground to powder without further treatment.

2.3 The hydrogenation of carbon dioxide to produce FA The reaction of CO2 hydrogenation was conducted in a batch reactor (100 mL of stainless autoclave). Typically, 50 mg catalyst was dispersed in 1.0 mol L−1 of aqueous KHCO3 solution (10 mL) or 10 mL of mixed solution of H2O and amines (3:1), a total pressure of 2.0 MPa (H2 : CO2 = 1:1) was charged. After 24 h, the reaction system was analyzed by 1H NMR spectroscopy with DMSO as internal standard in D2O.

3. Results 3.1 Synthesis and structures of the MoC@NxC catalysts. We developed a novel supramolecular self-assembly method to integrate ultrafine MoC nanoparticles into a carbon matrix with a large amount of exposed surface for possible reactions via the carbonization of assemblies (Fig. 1a and Figs. S1–S3 (online)) of PMo12 and melamine with the assistance of an excess amount of dicyandiamide. Highly dispersed MoC nanoparticles within connected carbon sheaths, according to the high-resolution transmission electron microscope (HRTEM) 4

observation (Figs. 1b, c and Fig. S4 (online)), demonstrated the key importance of the assembly process of PMo12 with melamine in keeping the MoC components from aggregation (Figs. S5, S6 (online)) during the carbonization process. X-ray energy-dispersive spectroscopy (XEDS) elemental mapping indicated the uniform distribution of N and Mo elements throughout the carbon layer (Fig. S7 (online)). The embedded MoC nanoparticles with an average diameter of 2.3 nm (Fig. S6c (online)) have a typical lattice spacing of 0.25 nm (Fig. 1c), which can be assigned to the (111) plane of δ-MoC according to the HRTEM image and the corresponding fast Fourier transform (FFT) pattern (Fig. 1c, inset). The X-ray absorption near-edge structure (XANES) and Fourier transform extended X-ray absorption fine structure (EXAFS) spectra (Figs. 1d–e, Figs. S8–12 and Table S1 (online)) combined with the powder X-ray diffraction (XRD; Fig. 1f and Fig. S13 (online)) results further revealed the successful synthesis of δ-MoC.

Fig. 1 Synthesis and microstructure analysis of the MoC@NxC catalysts. (a) The proposed synthetic process for the MoC@NxC catalysts. (b, c) The HRTEM images of a typical [email protected] sample. (d) XANES spectra of Mo foil, MoO2, MoO3, and [email protected] at the Mo-K edge. (e) k-Weighted EXAFS spectra (solid line) and the first- and second-shell fits (circles) of [email protected], k=1. (f) XRD patterns of the MoC@NxC catalysts (JCPDS No. 65-8092). (g–i) The

5

EELS spectra and corresponding N- and O-K edge spectra of a randomly selected δ-MoC nanoparticle. Insets: (c) The selected-area FFT pattern; (e) The unit cell structure of δ-MoC; (g) A TEM image of a selected δ-MoC nanoparticle (the white arrow indicated the scanning direction).

The high-resolution electron energy loss (EELS) spectra analysis of a randomly selected MoC nanoparticle (Fig. 1g) clearly indicated its core-shell structure with a Mo-rich core and a Mo-poor carbon shell. Most importantly, neither O-K edge (~533 eV) nor N-K edge (~404 eV) was detected in the EELS spectra of the MoC nanoparticle (Fig. 1h, i), suggesting a pure phase of MoC but excluding the existence of a major amount of molybdenum oxides or nitrides [27].

3.2 Catalytic performance of MoC@NxC catalysts for CO2 hydrogenation The high surface areas (Table S2, Figs. S14 and S15 (online)) of the MoC@NxC catalysts with varied nitrogen content (Fig. S16–S20 and Table S3 (online)) encouraged us to evaluate their catalytic performance (Fig. 2a and Table S4 (online)) in the CO2 hydrogenation reaction in an autoclave reactor filled with a mixed gas of CO2 and H2 (1:1, total pressure: 2 MPa). The blank reaction did not proceed without any catalyst. The pristine MoC (Fig. S21 (online)) gave a moderate yield of FA, suggesting the possible role of MoC component as active centers for CO2 hydrogenation. The mechanical mixture of MoC and NC slightly improved the conversion of CO2, even though the bare NC sample was inactive for the same reaction. Surprisingly, the MoC@NxC catalysts gave very high yields of FA without the formation of carbon monoxide or other possible byproducts (Figs. S22, S23 (online)). Increasing the nitrogen content of the NxC support gradually and significantly elevated the yield of FA over MoC@NxC catalysts with similar sizes (Fig. S24 (online)) and contents (Table S3 (online)) of MoC nanoparticles, speaking for the synergetic effect between MoC and NxC components. Such an interfacial promotion of the activation of CO2 and H2 was demonstrated experimentally by the ever lowered apparent activation energy of the CO2 hydrogenation reaction from 36.2 via 32.2 to 28.7 kJ mol−1 for [email protected], [email protected] and [email protected] (Fig. 2d), 6

respectively, which were all substantially lower than the theoretical value 305.4 kJ mol−1, dashed line in Fig. S25 (online)) [29]. Furthermore, we conducted additional isotopic labeling experiments and control reactions to confirm and quantify the carbon source of FA only from the CO2 gas (Fig. S26, S27 (online)) [30, 31]. The yield of H13COOH continuously increased with the reaction time for the reaction fed with

13CO

2

gas (Fig. S27b (online)), and

13C

labelled FA product was not detected in our catalytic system at the beginning (0 h) or only fed with

12CO

2

gas for 48 h (Fig. S27c (online)). All these results exclude the

possible carbon contamination caused by trimethylamine.

Figure 2. Catalytic performance of MoC@NxC catalysts. (a) The production of FA over differenct catalysts. (b) The influence of various bases on the FA production over the [email protected] catalyst. (c) The influence of temperature on the FA production and (d) the corresponding Arrhenius plots of MoC@NxC catalysts. (e) Time courses of the dehydrogenation reaction of FA over [email protected] and bench-marked Pd/CN catalyst [28]. (f) Time course (spheres) of the CO2 hydrogenation reaction and corresponding TOF values (circles) over the [email protected] catalyst.

The susceptibility of MoC materials to ambient air, as already described in Refs. [32-35], generates a tiny amount of surface molybdenum oxide according to the O 1s XPS spectra of all samples (Fig. S19 and Table S3 (online)). The inert feature of molybdenum oxide for CO2 reduction [36] (Entry 3 in Table S4 (online)) and comparable O contents in the [email protected] catalyst before and after reactions (Fig. 7

S28 (online)) unambiguously indicate the negligible effect of molybdenum oxide components on the promoted activity of [email protected] catalyst. We further confirmed and optimized the conversion of CO2 molecules over the [email protected] catalyst by optimizing the catalyst dosage (Fig. S29 (online)) and then screening various bases (Fig. 2b and Table S6 (online)), which are important for enhancing the solubility of CO2 in the reaction system for further catalytic transformation. The fact that the control reaction using CO2-free H2 gas (entry 2 in Table S6 (online)) in the presence of KHCO3 did not give even a trace amount of FA suggested the production of FA over the [email protected] catalyst from the hydrogenation of CO2. Besides the direct hydrogenation of CO2 molecules in liquid phase, there were also pioneering work on the conversion of HCO3− and other carbonates [37]. However, no product was detected in our catalytic system for the hydrogenation of various carbonates (Entry 2 in Table S6 (online)), rather speaking for a totally different reaction in this work as compared with the reduction of carbonates [38]. Among various inorganic and organic bases tested, triethylamine (NEt3) performed as the best base to promote the production of FA over [email protected] to 831 μmol. As the best-in-class catalyst in this work, the [email protected] catalyst was used for following optimization of the reaction parameters in the presence of NEt3. It is noted that K and some other cations may act as promoter to boost the activity of metal centers [39]. However, the possible effect of various additives on promoting the MoC was also kept fixed by using the same dosage and fixed catalyst loading, more precisely the loadings of MoC species. As a result, the improved part of the activity of optimized MoC/NxC could be reasonably attributed to the support effect. The yields of FA over the MoC@NxC catalysts were further measured as a function of temperature for a better understanding of the support-effect dominating reaction kinetics (Fig. 2c, d and Table S7 (online)). To our delight, the CO2 hydrogenation proceeded smoothly over the MoC@NxC catalysts at relatively low temperatures, as low as 70 °C for the [email protected] catalyst. The Arrhenius plots (Fig. 2d) of all MoC@NxC catalysts with good linear relationships of the logarithm between the 8

reaction rate constant and the inverse temperature indicated a single rate-limited reaction process, excluding the possibility of the unwanted dehydrogenation reaction of FA in our catalytic system. Indeed, [email protected] was totally inert in the FA solution (Fig. 2e) and without the problem of dehydrogenation of FA confronted by noble-metal catalysts [40-42]. It should be noted that a rapid decomposition of FA was observed over the noble-metal catalyst, exemplified by a bench-marked Pd/CN reported as an active catalyst for the transformation between CO2 and FA.

Figure 3. Properties of MoC@NxC-based Mott-Schottky heterojunction. (a) The CDD stereograms at the interface of the [email protected] model. (b) The number of electrons transferring from NxC supports to δ-MoC cluster. (c) The measured work functions (Φ) and (d) Mo 3d XPS spectra of pure MoC and the MoC@NxC samples. (e) The XANES spectra, (f) CO2-TPD spectra and (g) H2-TPD spectra of the MoC@NxC catalysts. Insets: (b) The calculated CDD stereograms; (c) A scheme of the rectifying Mott-Schottky contact of MoC and NxC; (e) The white line of MoC@NxC samples marked with arrows.

As an inexpensive but efficient catalyst, the [email protected] sample also presented excellent stability for long-term uses, well reflected by the continuously increased production of FA as a function of time and by the stable TOF values of the catalyst during the 48-hour reaction (Fig. 2f). Moreover, the morphology and the crystalline structure of the used [email protected] catalyst were also well maintained (Fig. S30, S31 (online)), promising its great potential as a sustainable catalyst for practical applications. 9

3.3 Roles of the MoC@NxC heterojunctions in CO2 hydrogenation The electronic structure and properties of the MoC-NxC nanoheterojunctions were carefully investigated via both theoretical and experimental methods. The density functional theory (DFT) simulation results first demonstrated the metallic nature of MoC (Fig. S32 (online)) and the gradually enlarged band gap of the NxC supports (Fig. S33 (online)) obtained by increasing the nitrogen dopant concentration. The combination of MoC and NxC together led to the formation of a rectifying contact (Fig. 3a), as directly presented by the electron-rich area of the MoC NPs and the electron-deficient area of the N-doped carbon supports in the charge density difference (CDD) stereograms (Fig. 3a, b and Fig. S34 (online)). The calculated number of electrons transferred from NxC to MoC components increased gradually from 0.04 electrons for [email protected] to 0.12 electrons for [email protected], leading to a lower work function for the [email protected] sample due to the Mott-Schottky effect as depicted in the inset of Fig. 3c. Such a trend of the lowering work function of MoC components induced by the support effect was then experimentally confirmed by the ultraviolet photoelectron spectroscopy (UPS) results (Fig. 3c and Fig. S35 (online)) and accompanied by the elevated conduction band position of the NxC supports, according to the Mott-Schottky plots (Fig. S36 (online)). Moreover, the largely enhanced electron enrichment of the [email protected] sample was demonstrated by a significant shift of its Mo 3d XPS peak to a lower binding energy as compared to pure MoC (Fig. 3d). In addition, detailed XANES results of various MoC@NxC catalysts with increased N contents exhibited similar absorption edges (Fig. 3e) but elevated white lines (marked with arrows in the inset of Fig. 3e) further confirm the similar oxidation state but increased electron density of Mo species [43-45]. All these results indicated our success in constructing a Schottky heterojunction composed of electron-rich MoC and electron-deficient NxC species. We further investigated the adsorption behavior (Fig. 4a, b) of reactant molecules at the interface of the MoC@NxC heterojunctions for a better 10

understanding of the real role of the Mott-Schottky effect in promoting CO2 hydrogenation. There is a consensus in the literature that more nitrogen dopants will increase the Lewis basicity of a carbon matrix, which is, however, not true in our MoC@NxC dyadic system. The amounts of Lewis basic sites (Fig. 3f and Figs. S37, S38 (online)) in MoC@NxC for absorbing CO2 molecules gradually decreased, again due to the reduced electron density of the NxC support from [email protected] via [email protected] to [email protected]. Notably, the desorption peak of CO2 over the [email protected] sample shifted to a lower temperature, suggesting a lower barrier for the activation of CO2 to benefit further catalysis.

Figure 4. Roles of MoC@NxC heterojunction in activating CO2. (a) The CDD stereograms after the introduction of a CO2 molecule onto the interfacial part of the MoC@NxC models. (b) The calculated adsorption energy of CO2 molecules adsorbed on the MoC@NxC catalysts. (c) The proposed reaction path over the bench-mark [email protected] catalyst on the basis of the energy

11

differences of all possible configurations. (d) The calculated Gibbs free energy diagram for the hydrogenation of adsorbed CO2 (*CO2) to *HOCO over the MoC@NxC heterojunctions. (e) The TOF values of the MoC@NxC catalysts at 140 °C. Insets: (b) The equilibrium distance from the adsorbed CO2 to the NxC support; (d) The calculated configurations after the formation *HOCO over the MoC@NxC catalysts.

Indeed, the theoretical simulation results (Fig. 4a) also demonstrated the enhanced preadsorption of CO2 molecules to the MoC species, accompanied by an apparent bending of the linear CO2 molecules, with the O=C=O bond angle between 127.2 and 128.2 ° (Table S8 (online)). The C-C bond formed between the C atom of CO2 and the surface C atom in the MoC cluster was forced by sp→sp2 hybridization, with a distance between 1.47 and 1.52 Å, suggesting a preferred adsorption of CO2 to MoC for all MoC@NxC samples. More importantly, the electron-rich MoC and electron deficient N-carbon support in [email protected], as the optimized sample, could polarize the CO2 molecule (as marked with a red arrow in Fig. 4a) via a manner like frustrated Lewis acid-base pairs [46]. Such a highly coupled configuration of [email protected] and CO2 with a distance of approximately 2.5 Å (Fig. 4b, inset) and thus the lowest absorption energy (−1.161 eV) (Fig. 4b) could largely promote the preadsorption of CO2 at the boundary part of [email protected], as already confirmed experimentally by the CO2-TPD results (Fig. 3e). Similarly, the enhanced pre-adsorption of nonpolar molecules was also available for binding H2 molecules, as reflected by a new and strong desorption peak in H2-TPD curve of the [email protected] catalyst at a relatively low temperature (Fig. 3g). The activation of CO2 molecules after the adsorption process at the rectifying interface dominated the selectivity to target product and the final conversion. We thus investigated the possible reaction paths (Fig. 4c) for CO2 hydrogenation at the boundary of MoC and NxC by DFT calculations. The C-O bond cleavage path with the first hydrogen atom added to two O sites of CO2 usually led to the formation of CO or methanol is not energetically favorable (Fig. 4c and Fig. S39 (online)) on typical MoC [47], matching well the trend of our experimental results (Fig. 2). The selective hydrogenation of the near-end O of preadsorbed CO2 for the formation of 12

*HOCO was, however, more favorable over our [email protected] dyad, as the most stable configuration among all possible ones (Fig. 4c). The highly polarized CO2 molecule at the rectify interface (Fig. 4a, right) largely lowered the Gibbs free energy for the conversion of *CO2 to *HOCO, according to the DFT calculation results (Fig. 4d). This further ensured the successive addition of another hydrogen atom to the carbon site of absorbed *HOCO, facilitating the activation of CO2 over [email protected] dyads, even under very mild conditions with a high selectivity to FA (Fig. S40 (online)). As the first example of noble-metal-free heterogeneous catalysts available for CO2 hydrogenation in liquid phase at a temperature as low as 70 °C, the [email protected] catalyst provided a TOF of 0.15 and 8.20 molFA molMoC−1 h−1 at 140 °C for reducing CO2 to FA, even comparable to some of noble-metal based nanocatalysts (Fig. 4e and Table S9 (online)).

4. Discussion and conclusions In summary, we successfully demonstrated the key role of electron-rich MoC nanoparticles in activating CO2 for further hydrogenation into FA. The rectifying contact formed at the interface of MoC nanoparticles and nitrogen-doped carbon was confirmed theoretically and then demonstrated experimentally to boost the adsorption and further activation of the gaseous molecules for the selective generation of FA. The optimal [email protected] sample with the most pronounced electron enrichment of MoC species could act as stable catalyst for highly efficient production of FA via CO2 hydrogenation, outperforming existing noble-metal-free nanocatalysts. This work not only opened up a new path to design and engineer efficient Schottky heterojunctions in low-cost and durable catalysts applied in the field of hydrogenation process but also advanced the research of direct CO2 reduction.

Conflict of interest The authors declare that they have no conflict of interest.

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Acknowledgments This work was supported by the National Natural Science Foundation of China (21722103, 21720102002, 21673140, 21673273 and 21872163), the Shanghai Basic Research Program (16JC1401600), the SJTU-MPI partner group and the Open Research Fund of the State Key Laboratory of Inorganic Synthesis and Preparative Chemistry (Jilin University, Grant No. 2018-09). The authors thank Shanghai Synchrotron Radiation Facility for providing beam time (BL14W1).

Author contributions Xin-Hao Li and Hong-Hui Wang designed the experiments. Hong-Hui Wang conducted the synthesis of the MoC@NxC catalysts, carried out all corresponding characterizations, analysis and the catalytic performance experiments and result analysis. Shi-Nan Zhang and Tian-Jian Zhao helped to conduct DFT calculations and computational results analysis. Yong-Xin Liu and Juan Su offered help to the result analysis. Xi Liu helped to carry out the EELS analysis. Xin-Hao Li and Hong-Hui Wang co-wrote the original manuscript. Jie-Sheng Chen and Xin-Hao Li oversaw all research phases and revised the manuscript. All authors discussed the results and commented on the manuscript.

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Hong-Hui Wang received the bachelor degree at Huazhong University of Science and Technology majoring in Chemical Engineering and Technology from 2011 to 2015 and now is studying for a Ph.D. degree of Applied Chemistry in the School of Chemistry and Chemical Engineering at Shanghai Jiao Tong University. His research interest centers on the design and development of inorganic nanomaterials applied in the field of energy and environment.

Xin-Hao Li is currently a professor in Shanghai Jiao Tong University (2013– present). He completed each of his academic degrees from Jilin University from 1999 to 2009, receiving his Ph.D. in 2009 with professor Jie-Sheng Chen. He then joined Prof. Markus Antonietti’s group as a postdoctor at the MaxPlanck Institute of Colloids and Interfaces from 2009 to 2012. His current 19

scientific interest is mainly focused on the development of Mott-Schottky catalysts for energy and environmental science.

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