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C octahedral and OER composite catalyst
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Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst Jue Wang a, Xiangyang Zhou b, Bing Li b,*, Daijun Yang b, Hong Lv b, Qiangfeng Xiao b, Pingwen Ming b, Xuezhe Wei b, Cunman Zhang b a
Postdoctoral Mobile Station of Mechanical Engineering & School of Automotive Studies, Tongji University, 4800 Cao’an Road, Shanghai, 201804, China b School of Automotive Studies & Clean Energy Automotive Engineering Center, Tongji University, 4800 Cao’an Road, Shanghai, 201804, China
highlights
graphical abstract
PtNi/C Oct and OER catalyst are prepared and mixed to composite catalyst. MEA is prepared with PtNi/C Oct in cathode and composite catalyst in anode. This MEA shows good power generation
performance
and
cell
reversal durability. This work realizes actual application of Pt-based octahedral catalyst in PEMFC.
article info
abstract
Article history:
In order to obtain a fuel cell with both enhanced power generation performance and cell
Received 9 October 2019
reversal resistance, the composite catalyst consisting of the self-made PtNi/C octahedral
Received in revised form
and the oxygen evolution reaction (OER) catalyst IrO2 and RuO2 is mixed and applied in the
20 December 2019
anode, and the only octahedral catalyst is employed as the cathode to prepare the mem-
Accepted 8 January 2020
brane electrode assembly (MEA). The electrochemical activity of the composite catalyst
Available online xxx
decreases slightly, but its performance retention after the accelerated durability test (ADT) is higher. In the single cell test, the MEA fabricated using the composite catalyst maintains
Keywords:
good single cell power generation performance. Compared with the control fabricated with
PtNi octahedral
Pt/C (JM), the cell voltage at 1 A cm2 and the maximum power density are increased by
Oxygen reduction reaction (ORR)
23 mV and 119 mW cm2, respectively. Especially, its durability under continuous cell
Oxygen evolution reaction (OER)
reversal condition is also improved significantly, and the holding time is prolonged by 1 h.
catalyst
This work realizes the transformation of the octahedral catalyst from the laboratory
Membrane electrode assembly
* Corresponding author. E-mail address: [email protected] (B. Li). https://doi.org/10.1016/j.ijhydene.2020.01.054 0360-3199/© 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Wang J et al., Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.054
2
international journal of hydrogen energy xxx (xxxx) xxx
(MEA)
research to the actual application, and solves the difficulties in fuel cell application, and
Cell reversal
promotes its commercialization. © 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Fuel cell is a power generation device that can transform the chemical energy produced by the chemical reaction into electrical energy by being continuously supplied with fuel. Among varieties of fuel cells, proton exchange membrane fuel cell (PEMFC) shows great potential in the field of transportation for example vehicles because of its advantages of high power density, stable solid electrolyte, fast start-up, good thermoelectric cycle performance and low operating temperature [1e4], and thus its application in vehicles has attracted more and more attention. However, the shortcomings of PEMFC in cost, performance and supporting infrastructure still restrict its development [5]. Therefore, one of the major development trends of PEMFC is to overcome above difficulties in the automotive application. In PEMFC, electrode reactions in both cathode and anode are difficult to occur under general conditions because of their poor kinetic characteristics. Therefore, the catalysts must be introduced to decrease the activation energy so that the electrode reactions can occur. Pt is the most common PEMFC catalyst, but its high cost and unsatisfactory activity and durability have been main obstacles for the commercialization of PEMFC [6,7]. To achieve better single cell performance, the investigations on cathode and anode catalysts have different emphasis in view of the difference between the two electrode reactions. For oxygen reduction reaction (ORR) in cathode, owing to its slow kinetics, the cathodic overpotential can reach 300 mV under open circuit condition [8], and more attention is paid to improving the ORR activity of cathode catalyst. On the one hand, alloying is employed to enhance the activity and reduce the use of Pt; on the other hand, the structure of the Pt-based catalyst is designed at the nanoscale to improve the Pt utilization by increasing the mass activity of catalyst, and various low-Pt [9e11] and specific morphology catalysts [12e21] have appeared in succession. Among them, Pt alloy octahedral catalysts with considerable active (111) facets [22e24] exhibit outstanding ORR activity [25e29], which is helpful to meet requirements of cathode catalysts for improving activity and reducing cost, and thus have attracted more attention. In anode, because Pt has good absorption and catalytic capacity for hydrogen, the anode overpotential is very low, and Pt can play a good role in catalyzing hydrogen oxidation reaction (HOR). Therefore, there is no high requirement for the activity of the anode catalyst, and it is hoped that it has a better durability. Especially in the actual fuel cell, when the anode is supplied with insufficient fuel, the anode polarization will occur, and the anode potential will increase, even exceeds the cathode potential, that is, the cell reversal occurs [30,31], which makes the electrons and protons that are required by the oxygen reduction reaction in the cathode
supplied by water electrolysis and carbon oxidation [32,33]. The corrosion of the carbon supports can cause the shedding, agglomeration and sintering of Pt [7,34,35], which will decrease the performance of the catalyst. Moreover, the damage of the carbon corrosion is more serious for the anode owing to a lower Pt loading and thinner thickness of catalyst layer compared with the cathode. In order to alleviate the damage of the cell reversal, besides adopting the proper system control strategies to avoid insufficient fuel supply [36] and employing the support materials with high corrosion resistance, it is another effective method to add the oxygen evolution reaction (OER) catalyst into the anode to prevent the corrosion of the carbon supports by promoting the oxidation of water [37e39]. As it is difficult for non-precious metals to meet the requirements of OER catalyst for good activity and stability in high acid and high potential operation environment, few research results on non-precious metal substitutes were reported [40,41]. At present, precious metal OER catalysts are still mainly employed. Among various OER catalysts, RuO2 has an excellent catalytic activity [42,43], but its durability is poor [44]. The activity of IrO2 is slightly lower than that of RuO2, but its chemical stability is obviously better. In order to give consideration to the high activity of Ru and the high stability of Ir, the mixture of the self-made IrO2 and RuO2 is employed as OER catalyst. In this work, the self-made PtNi/C octahedral catalyst (PtNi/C Oct) with high ORR activity in the light of our previous research [45] is employed in the cathode to improve the cathode reaction kinetics, and the composite catalyst consisting of PtNi/C Oct and OER catalysts is used in the anode to ameliorate the cell reversal durability of the single cell, and the membrane electrode assembly (MEA) with good power generation performance and improved cell reversal resistance is successfully obtained. Compared with the control fabricated using Pt/C (JM) (Johnson Matthey HiSpec 4000) in both electrodes, its cell voltage at 1 A cm2 and maximum power density are increased by 23 mV and 119 mW cm2, respectively. Especially, the holding time of this MEA is 1 h longer than that fabricated using only PtNi/C Oct and its performance retention rate is also higher under continuous cell reversal condition. This work not only covers the shortage of the investigation on the octahedral catalyst in single cell application, but also improves the power generation performance and the cell reversal durability of PEMFC, which is valuable to the fuel cell application in vehicles.
Experimental section Preparation of PtNi/C Oct Based on the structure-directing agent method in our previous work [45], PtNi/C Oct with 30 wt% Pt and 10 wt% Ni was
Please cite this article as: Wang J et al., Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.054
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Fig. 1 e (a, b, c) TEM images of the composite catalyst consisting of PtNi/C Oct and IrO2, RuO2, (deg) the EDS mapping images of the composite catalyst, (h) TEM images of IrO2, (i) TEM images of RuO2.
synthesized. The reaction mixture was produced by uniformly dispersing 4 mM Pt(acac)2, 10 mM Ni(acac)2, 4 mM cetyltrimethylammonium bromide (CTAB) and XC-72 carbon black
into dimethylfomamide (DMF) solution, and then heated in an autoclave at 160 C for 12 h. After washed and dried, PtNi/C Oct sample was obtained, and its yield can reach 88%e92%.
Please cite this article as: Wang J et al., Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.054
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Table 1 e The average numbers of transferred electrons n of PtNi/C Oct calculated according to the K-L plots. Potentials (vs. RHE)/V 0.3 0.5 0.7
1/B
n
9.1918 9.1351 9.4988
3.902 3.926 3.776
Preparation of OER catalyst IrO2 and RuO2 were prepared by Adams melting method [46]. H2IrCl6 and RuCl3 were mixed with excess NaNO3 fine grains, respectively, and then the two mixtures were dried to obtain the precursor powders. The powders were heated in a muffle furnace at 400 C for 1 h. After cooled and washed to neutrality with deionized water, IrO2 and RuO2 powders were finally obtained by freeze-drying. Fig. 2 e XRD spectra of the composite catalyst.
Fabrication of MEAs The catalyst slurry was obtained by dispersing catalyst and 5% Nafion solution (mass ratio of Nafion to carbon is 1: 1.8) into water and isopropanol (volume ratio of 1: 1). This slurry was sprayed onto a membrane of 25 cm2 (GORE®), and then the gas diffusion layers (SGL, 25BC) were fixed to both sides of the assprayed membrane to produce a MEA. To improve the comprehensive single cell performance, the MEA was fabricated using the composite catalyst that consists of PtNi/C Oct and OER catalysts (IrO2 and RuO2 account for 6% of the total mass, respectively) in the anode, and only PtNi/C Oct in the cathode. Two controls were obtained using only PtNi/C Oct or Pt/C (JM) in both electrodes, respectively. The Pt loadings of the cathode and the anode in all the three MEAs are 0.4 and 0.2 mgPt cm2.
Physical characterization The structure of the catalyst and its morphology changes after durability test were analyzed by transmission electron microscopy (TEM). Scanning electron microscopy (SEM) was employed to observe the surface structure of MEA catalyst layer and the change after the cell reversal test. Energy dispersion spectrum (EDS) was employed to investigate the distribution of the components in the composite catalyst, and was also employed to investigate the changes of element composition and distribution on the surface of MEA catalyst layer after the cell reversal test so as to analyze the reasons for the degradation of MEA performance. The crystallinity of the composite catalyst was determined by X-ray diffraction (XRD).
Electrochemical evaluation
Fig. 3 e (a) LSV curves of PtNi/C Oct at different rotating speeds and (b) K-L plots under different potentials.
The electrochemical tests were conducted by a rotating disc electrode (RDE) technique. Cyclic voltammetry (CV), linear sweep voltammetry (LSV) and accelerated durability testing (ADT) were conducted to estimate the electrochemical activity and the durability of the catalysts. The preparation of the catalyst ink, the composition of the three-electrode system and the details of the electrochemical tests refer to our asreported work [45].
Please cite this article as: Wang J et al., Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.054
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analyze the tolerance of single cell under cell reversal condition. MEAs were kept under a reverse current of 0.2 A cm2 with cell temperature of 80 C, relative humidity (RH) of 100%, cathode and anode supplied with air and N2. The voltage-time (V-t) curves of the single cells were recorded when the cell voltages drop from open-circuit voltage to 2.0 V, and then the polarization curves were also measured to evaluate the changes of the single cell performances before and after the cell reversal test.
Result and discussion To find out the effect of adding OER catalyst on the structure and property of the composite catalyst, the physical and electrochemical characterizations were carried out.
Physical characterization of the composite catalyst Fig. 1a and b are TEM images of the composite catalyst consisting of PtNi/C Oct, IrO2 and RuO2. Besides the light gray carbon supports and the dark gray PtNi/C Oct nanocrystals of about 6 nm as shown in the HRTEM image embedded in Fig. 1b, the fine equiaxed IrO2 grains of 3 nm (Fig. 1h) and the larger black RuO2 particles with size range from 20 to 50 nm (Fig. 1i) can be also observed. Fig. 1deg are the EDS mapping images of the composite catalyst, and it exhibits that IrO2 and RuO2 are uniformly dispersed in PtNi/C Oct, and especially IrO2 with smaller size shows a higher dispersion degree, which provides a guarantee for better promoting water oxidation and preventing carbon corrosion. The XRD spectra of the composite catalyst are shown in Fig. 2. The diffraction peaks of (111), (200), (220) and (311) facets of PtNi octahedra appear at 41 , 47 , 69 and 83 , respectively. The larger diffraction angles compared with pure Pt demonstrate the formation of PtNi alloy phase. The sharp diffraction peaks at 28 , 35 and 54 correspond to (110), (101) and (211) facets of IrO2 and RuO2 rutile phase, and their (111) diffraction peaks near 40 are covered by the PtNi(111) peak. Combining the above TEM results, because the diffraction peak positions of IrO2 and RuO2 are similar, the peaks of IrO2 with smaller size are wider and flatter, and the peaks of RuO2 with larger size are sharper. Therefore, the IrO2 peaks are covered, the RuO2 peaks with very small full width at half maximum (FWHM) can be obviously observed on the whole. Fig. 4 e (a) CV curves of the composite catalyst and PtNi/C Oct, (b) the comparison of CV curves of the composite catalyst before and after 2000 cycles ADT, (c) the comparison of ECSA changes of the composite catalyst, PtNi/C Oct and Pt/C (JM) before and after ADT.
Characterization and cell reversal durability test of MEAs All MEAs were performed the same single cell tests as following. The polarization curves were obtained by the steps as reported in our work [45]. Cell reversal test is employed to
Electrochemical characterization of the catalysts Fig. 3a shows the LSV curves of PtNi/C Oct at different rotating speeds. All the four LSV curves are composed of three different regions. When the potential is less than 0.54 V, it is the diffusion control region; when the potential is higher than 0.75 V, it is the dynamic control region; when the potential is between 0.54 V and 0.75 V, it is the mixed control region. The limiting current density of LSV curve in the diffusion control region increases with the increase of the electrode rotating speed. The ORR kinetics of PtNi/C Oct is analyzed by KutkayLewitic (K-L) equation. The K-L plots under different potentials are presented in Fig. 3b, and the average numbers of
Please cite this article as: Wang J et al., Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.054
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Fig. 5 e (a) SEM image of the anode catalyst layer of the MEA fabricated using the composite catalyst and the EDS mapping of (b) Pt, (c) Ni, (d) Ir, (e) Ru.
Fig. 6 e The comparison of performance curves of MEA fabricated with PtNi/C Oct in cathode and the composite catalyst in anode and the controls prepared with only PtNi/ C Oct or Pt/C (JM).
oxygen. Therefore, as mentioned in our previous work [45], the mass activity and specific activity of PtNi/C Oct employed in this work reach 6.1 and 6.6 times of Pt/C (JM), respectively, so its application in the cathode is conducive to better power generation performance of MEA. Fig. 4a shows the CV curves of the composite catalyst and PtNi/C Oct. The calculated electrochemically active surface area (ECSA) of the composite catalyst is 42.1 m2 g1 Pt , which is lower than that of the latter, revealing that the 6.6 m2 g1 Pt surface of PtNi/C Oct crystal still plays a catalytic role in the composite catalyst, but the exposure of active sites is affected by the addition of OER catalyst, so the ECSA of the composite catalyst slightly decreases. Fig. 4b exhibits the change of CV curves of the composite catalyst before and after ADT. After 2000 cycles, its ECSA decreases by 21.4% as shown in Fig. 4c. According the comparison of CV curves of PtNi/C Oct and Pt/C (JM) before and after ADT reported in our previous work [45], the ECSA attenuations
transferred electrons n and the curve slopes 1/B calculated according to the K-L equation are listed in Table 1. Each n value is close to 4, indicating that the ORR on PtNi/C Oct mainly follows the four-electron reaction mechanism. Compared with the two-electron reaction on pure Pt surface, four-electron reaction is more favorable for the reduction of
Table 2 e The comparison of power generation performances of MEAs fabricated using the composite catalyst, PtNi/C Oct and Pt/C (JM). Anode catalyst
PtNi/C Oct þ IrO2 þ RuO2 PtNi/C Oct Pt/C JM
Maximum power density (mW cm2)
Cell voltage @1 A cm2 (V)
923.4
0.672
954.0 804.4
0.679 0.649
Fig. 7 e The comparison of the V-t curves of the MEA prepared using the composite catalyst in anode and the control prepared with only PtNi/C Oct during the process of the cell reversal.
Please cite this article as: Wang J et al., Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.054
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Fig. 8 e The comparison of performance curves of (a) the MEA prepared using the composite catalyst in anode and (b) the control prepared with only PtNi/C Oct before and after the cell reversal test, and the changes of (c) cell voltage at 1 A cm¡2 and (d) maximum power density.
of two controls are 22.8% and 38.9% under the same test conditions, respectively, indicating that the composite catalyst has higher electrochemical stability. In previous work [45], we have investigated the reasons for the activity attenuations of PtNi/C Oct during ADT. It is believed that its degradation should impute to the loss of alloy (111) facets caused by the change of octahedral morphology and the Pt loss owing to the carbon corrosion. The addition of OER catalyst can inhibit the carbon corrosion to a certain extent, so that the durability of the composite catalyst can be improved. According to the above physical characterization results, IrO2 and RuO2 are successfully added into PtNi/C Oct by
physical mixing method and ensure a certain degree of dispersion. The addition of OER catalyst has a certain effect on the electrochemical performance of the composite catalyst, making its initial activity slightly reduced and its electrochemical durability slightly improved.
Power generation performance of the composite catalyst for PEMFC anode To investigate the application potential of the MEA consisting of highly active PtNi/C Oct in cathode and the composite catalyst in anode, its power generation performance in the
Fig. 9 e TEM images of (a) the composite catalyst and (b) PtNi/C Oct in MEA anodes after the cell reversal test. Please cite this article as: Wang J et al., Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.054
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Fig. 10 e SEM images and EDS of the anode catalyst layer of the MEA prepared using the composite catalyst (a, c, e) before and (b, d, f) after the cell reversal test.
actual single cell was tested and compared with the two controls. Fig. 5 is SEM image of the anode in the MEA prepared by the composite catalyst and its EDS mapping images. The surface of the anode is fairly flat before the test, and the four metal elements, Pt, Ni, Ir and Ru are uniformly distributed, demonstrating that PtNi/C Oct and OER catalyst are well-distributed
in the catalyst layer, which will be beneficial to improving the power generation performance of single cell and protecting the carbon supports. Fig. 6 exhibits the performance curves of the three MEAs, and their single cell performance parameters are summarized in Table 2. The cell voltage at 1 A cm2 of MEA fabricated using the composite catalyst reaches 0.672 V and its maximum
Please cite this article as: Wang J et al., Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.054
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power density is 923.4 mW cm2, which are slightly lower than those prepared using only PtNi/C Oct. Its slightly lower power generation performance may be ascribed to the increase of catalyst layer thickness and the changes of hydrophilicity resulted from the addition of OER catalyst. However, its power generation performance still has obvious advantages compared with the control prepared using Pt/C (JM), and its above two parameters are improved by 23 mV and 119 mW cm2, respectively. As mentioned in Section Electrochemical characterization of the catalysts, it is because PtNi/C Oct with enhanced ORR activity can better meet the requirement of the cathode for high catalytic activity.
Cell reversal durability of MEA fabricated with the composite catalyst in anode The cell reversal durability tests of MEA fabricated using the composite catalyst and the control prepared with only PtNi/ C Oct were conducted, and their V-t curves are presented in Fig. 7. Because the anode is supplied with N2 and fuel is insufficient, the control can only provide electrons and protons to the cathode by water electrolysis and carbon oxidation in the anode. The whole process of reducing the cell voltage to 0.2 V only takes about 11 min. For MEA fabricated using the composite catalyst, with the anode potential gradually increasing to water oxidation potential of 1.23 V, electrons and protons are provided to the cathode by the rapid water oxidation in the presence of OER catalyst, which will avoid the corrosion of the carbon supports. Therefore, a relatively flat platform appears in this region of the V-t curve, and the cell voltage does not significantly decrease. At this stage, the anode potential is as high as 1.5 Ve1.7 V, and the increase of the anode potential causes that the cell voltage decreases from 0.6 V to 0.8 V. As the rate of water oxidation can no longer meet the need of the cathode reaction, the carbon corrosion begins to occur significantly. The cell voltage continues to decrease from 0.8 V and the slope of the V-t curve gradually increases until the cell voltage drops to 2.0 V. The whole cell reversal test lasts 71 min. Fig. 8 compares the power generation performance of the two MEAs before and after the cell reversal test. After tests, their cell voltages at 1 A cm2 and maximum power densities obviously decline. For the one fabricated using the composite catalyst, above two parameters decrease by 104 mV and 266.8 mW cm2, and the attenuation rates are 15.5% and 28.9%, respectively. For the control, they decrease by 135 mV and 335.2 mW cm2 with the attenuation rates of 19.9% and 35.1%, respectively, indicating that the performance degradation of the MEA prepared with the composite catalyst is still lower, although the cell reversal process is prolonged by 1 h, which also demonstrates that the application of the composite catalyst in the anode can improve the cell reversal resistance of the single cell. Fig. 9 show TEM images of the anode catalysts in the two MEAs after the cell reversal test. In the right image, light gray spherical carbon particles can be hardly observed, and serious carbon corrosion causes more obvious agglomeration of nanocrystals. In the left image, the carbon particles can still be
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observed, indicating that the addition of OER catalyst slows down the corrosion of the carbon supports, so the performance retention rate of MEA fabricated using the composite catalyst is higher after test. The SEM and EDS images of the MEA anode fabricated with the composite catalyst before and after the cell reversal test are presented in Fig. 10. After test, the surface of the anode catalyst layer becomes rough and many pits caused by the carbon corrosion appear. Because the thickness of the catalyst layer should be greater than the detection depth of EDS, all fluorine element comes from the ionomer Nafion added to the catalyst slurry. According to the EDS results shown in Fig. 10e and f, it can be found that the C and Pt contents relative to F significantly decrease after the cell reversal test, demonstrating that the corrosion of the carbon supports and the loss of the active components occur. It indicates that the carbon corrosion is still unavoidable during such a long cell reversal process despite adding OER catalyst. However, during the actual vehicle driving process, the insufficient fuel supply can be usually found in time, so the cell reversal generally occurs instantaneously and lasts very short. Therefore, the addition of OER catalyst such as IrO2 and RuO2 can still effectively inhibit the irreversible damage caused by the cell reversal. Combining above results of the single cell test, it can be proved that the MEA fabricated with highly active PtNi/C Oct in the cathode and the composite catalyst in the anode obviously improves the power generation performance and cell reversal resistance of the single cell.
Conclusion In this work, the MEA with both enhanced power generation performance and good cell reversal durability is successfully prepared using highly active PtNi/C Oct in the cathode and the composite catalyst containing PtNi/C Oct and OER catalyst in the anode. Its power generation performance is higher than the control fabricated with Pt/C (JM), and the cell voltage at 1 A cm2 and the maximum power density are increased by 23 mV and 119 mW cm2. Especially the holding time of MEA fabricated with the composite catalyst is prolonged by 1 h under continuous cell reversal condition, and its performance retention rate after test is also higher, revealing that the cell reversal tolerance of MEA is effectively improved. These results demonstrate that this work not only achieves the actual single cell application of the octahedral catalyst, but also effectively reduces the damage caused by the cell reversal while ensuring good power generation performance. This work has a certain practical significance to promote the commercialization of PEMFC.
Acknowledgement The authors appreciate the National Natural Science Foundation of China (No.21676204).
Please cite this article as: Wang J et al., Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.054
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exploration of PtNi/C octahedral nanocrystal as practical PEMFC cathode catalyst. J Power Sources 2018;406:118e27. [46] Adams R, Shriner R. Platinum oxide as a catalyst in the reduction of organic compounds. III. Preparation and properties of the oxide of platinum obtained by the fusion of chloroplatinic acid with sodium nitratel. J Am Chem Soc 1923;45(9):2171e9.
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Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst Jue Wang a, Xiangyang Zhou b, Bing Li b,*, Daijun Yang b, Hong Lv b, Qiangfeng Xiao b, Pingwen Ming b, Xuezhe Wei b, Cunman Zhang b a
Postdoctoral Mobile Station of Mechanical Engineering & School of Automotive Studies, Tongji University, 4800 Cao’an Road, Shanghai, 201804, China b School of Automotive Studies & Clean Energy Automotive Engineering Center, Tongji University, 4800 Cao’an Road, Shanghai, 201804, China
highlights
graphical abstract
PtNi/C Oct and OER catalyst are prepared and mixed to composite catalyst. MEA is prepared with PtNi/C Oct in cathode and composite catalyst in anode. This MEA shows good power generation
performance
and
cell
reversal durability. This work realizes actual application of Pt-based octahedral catalyst in PEMFC.
article info
abstract
Article history:
In order to obtain a fuel cell with both enhanced power generation performance and cell
Received 9 October 2019
reversal resistance, the composite catalyst consisting of the self-made PtNi/C octahedral
Received in revised form
and the oxygen evolution reaction (OER) catalyst IrO2 and RuO2 is mixed and applied in the
20 December 2019
anode, and the only octahedral catalyst is employed as the cathode to prepare the mem-
Accepted 8 January 2020
brane electrode assembly (MEA). The electrochemical activity of the composite catalyst
Available online xxx
decreases slightly, but its performance retention after the accelerated durability test (ADT) is higher. In the single cell test, the MEA fabricated using the composite catalyst maintains
Keywords:
good single cell power generation performance. Compared with the control fabricated with
PtNi octahedral
Pt/C (JM), the cell voltage at 1 A cm2 and the maximum power density are increased by
Oxygen reduction reaction (ORR)
23 mV and 119 mW cm2, respectively. Especially, its durability under continuous cell
Oxygen evolution reaction (OER)
reversal condition is also improved significantly, and the holding time is prolonged by 1 h.
catalyst
This work realizes the transformation of the octahedral catalyst from the laboratory
Membrane electrode assembly
* Corresponding author. E-mail address: [email protected] (B. Li). https://doi.org/10.1016/j.ijhydene.2020.01.054 0360-3199/© 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Wang J et al., Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.054
2
international journal of hydrogen energy xxx (xxxx) xxx
(MEA)
research to the actual application, and solves the difficulties in fuel cell application, and
Cell reversal
promotes its commercialization. © 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Fuel cell is a power generation device that can transform the chemical energy produced by the chemical reaction into electrical energy by being continuously supplied with fuel. Among varieties of fuel cells, proton exchange membrane fuel cell (PEMFC) shows great potential in the field of transportation for example vehicles because of its advantages of high power density, stable solid electrolyte, fast start-up, good thermoelectric cycle performance and low operating temperature [1e4], and thus its application in vehicles has attracted more and more attention. However, the shortcomings of PEMFC in cost, performance and supporting infrastructure still restrict its development [5]. Therefore, one of the major development trends of PEMFC is to overcome above difficulties in the automotive application. In PEMFC, electrode reactions in both cathode and anode are difficult to occur under general conditions because of their poor kinetic characteristics. Therefore, the catalysts must be introduced to decrease the activation energy so that the electrode reactions can occur. Pt is the most common PEMFC catalyst, but its high cost and unsatisfactory activity and durability have been main obstacles for the commercialization of PEMFC [6,7]. To achieve better single cell performance, the investigations on cathode and anode catalysts have different emphasis in view of the difference between the two electrode reactions. For oxygen reduction reaction (ORR) in cathode, owing to its slow kinetics, the cathodic overpotential can reach 300 mV under open circuit condition [8], and more attention is paid to improving the ORR activity of cathode catalyst. On the one hand, alloying is employed to enhance the activity and reduce the use of Pt; on the other hand, the structure of the Pt-based catalyst is designed at the nanoscale to improve the Pt utilization by increasing the mass activity of catalyst, and various low-Pt [9e11] and specific morphology catalysts [12e21] have appeared in succession. Among them, Pt alloy octahedral catalysts with considerable active (111) facets [22e24] exhibit outstanding ORR activity [25e29], which is helpful to meet requirements of cathode catalysts for improving activity and reducing cost, and thus have attracted more attention. In anode, because Pt has good absorption and catalytic capacity for hydrogen, the anode overpotential is very low, and Pt can play a good role in catalyzing hydrogen oxidation reaction (HOR). Therefore, there is no high requirement for the activity of the anode catalyst, and it is hoped that it has a better durability. Especially in the actual fuel cell, when the anode is supplied with insufficient fuel, the anode polarization will occur, and the anode potential will increase, even exceeds the cathode potential, that is, the cell reversal occurs [30,31], which makes the electrons and protons that are required by the oxygen reduction reaction in the cathode
supplied by water electrolysis and carbon oxidation [32,33]. The corrosion of the carbon supports can cause the shedding, agglomeration and sintering of Pt [7,34,35], which will decrease the performance of the catalyst. Moreover, the damage of the carbon corrosion is more serious for the anode owing to a lower Pt loading and thinner thickness of catalyst layer compared with the cathode. In order to alleviate the damage of the cell reversal, besides adopting the proper system control strategies to avoid insufficient fuel supply [36] and employing the support materials with high corrosion resistance, it is another effective method to add the oxygen evolution reaction (OER) catalyst into the anode to prevent the corrosion of the carbon supports by promoting the oxidation of water [37e39]. As it is difficult for non-precious metals to meet the requirements of OER catalyst for good activity and stability in high acid and high potential operation environment, few research results on non-precious metal substitutes were reported [40,41]. At present, precious metal OER catalysts are still mainly employed. Among various OER catalysts, RuO2 has an excellent catalytic activity [42,43], but its durability is poor [44]. The activity of IrO2 is slightly lower than that of RuO2, but its chemical stability is obviously better. In order to give consideration to the high activity of Ru and the high stability of Ir, the mixture of the self-made IrO2 and RuO2 is employed as OER catalyst. In this work, the self-made PtNi/C octahedral catalyst (PtNi/C Oct) with high ORR activity in the light of our previous research [45] is employed in the cathode to improve the cathode reaction kinetics, and the composite catalyst consisting of PtNi/C Oct and OER catalysts is used in the anode to ameliorate the cell reversal durability of the single cell, and the membrane electrode assembly (MEA) with good power generation performance and improved cell reversal resistance is successfully obtained. Compared with the control fabricated using Pt/C (JM) (Johnson Matthey HiSpec 4000) in both electrodes, its cell voltage at 1 A cm2 and maximum power density are increased by 23 mV and 119 mW cm2, respectively. Especially, the holding time of this MEA is 1 h longer than that fabricated using only PtNi/C Oct and its performance retention rate is also higher under continuous cell reversal condition. This work not only covers the shortage of the investigation on the octahedral catalyst in single cell application, but also improves the power generation performance and the cell reversal durability of PEMFC, which is valuable to the fuel cell application in vehicles.
Experimental section Preparation of PtNi/C Oct Based on the structure-directing agent method in our previous work [45], PtNi/C Oct with 30 wt% Pt and 10 wt% Ni was
Please cite this article as: Wang J et al., Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.054
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Fig. 1 e (a, b, c) TEM images of the composite catalyst consisting of PtNi/C Oct and IrO2, RuO2, (deg) the EDS mapping images of the composite catalyst, (h) TEM images of IrO2, (i) TEM images of RuO2.
synthesized. The reaction mixture was produced by uniformly dispersing 4 mM Pt(acac)2, 10 mM Ni(acac)2, 4 mM cetyltrimethylammonium bromide (CTAB) and XC-72 carbon black
into dimethylfomamide (DMF) solution, and then heated in an autoclave at 160 C for 12 h. After washed and dried, PtNi/C Oct sample was obtained, and its yield can reach 88%e92%.
Please cite this article as: Wang J et al., Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.054
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Table 1 e The average numbers of transferred electrons n of PtNi/C Oct calculated according to the K-L plots. Potentials (vs. RHE)/V 0.3 0.5 0.7
1/B
n
9.1918 9.1351 9.4988
3.902 3.926 3.776
Preparation of OER catalyst IrO2 and RuO2 were prepared by Adams melting method [46]. H2IrCl6 and RuCl3 were mixed with excess NaNO3 fine grains, respectively, and then the two mixtures were dried to obtain the precursor powders. The powders were heated in a muffle furnace at 400 C for 1 h. After cooled and washed to neutrality with deionized water, IrO2 and RuO2 powders were finally obtained by freeze-drying. Fig. 2 e XRD spectra of the composite catalyst.
Fabrication of MEAs The catalyst slurry was obtained by dispersing catalyst and 5% Nafion solution (mass ratio of Nafion to carbon is 1: 1.8) into water and isopropanol (volume ratio of 1: 1). This slurry was sprayed onto a membrane of 25 cm2 (GORE®), and then the gas diffusion layers (SGL, 25BC) were fixed to both sides of the assprayed membrane to produce a MEA. To improve the comprehensive single cell performance, the MEA was fabricated using the composite catalyst that consists of PtNi/C Oct and OER catalysts (IrO2 and RuO2 account for 6% of the total mass, respectively) in the anode, and only PtNi/C Oct in the cathode. Two controls were obtained using only PtNi/C Oct or Pt/C (JM) in both electrodes, respectively. The Pt loadings of the cathode and the anode in all the three MEAs are 0.4 and 0.2 mgPt cm2.
Physical characterization The structure of the catalyst and its morphology changes after durability test were analyzed by transmission electron microscopy (TEM). Scanning electron microscopy (SEM) was employed to observe the surface structure of MEA catalyst layer and the change after the cell reversal test. Energy dispersion spectrum (EDS) was employed to investigate the distribution of the components in the composite catalyst, and was also employed to investigate the changes of element composition and distribution on the surface of MEA catalyst layer after the cell reversal test so as to analyze the reasons for the degradation of MEA performance. The crystallinity of the composite catalyst was determined by X-ray diffraction (XRD).
Electrochemical evaluation
Fig. 3 e (a) LSV curves of PtNi/C Oct at different rotating speeds and (b) K-L plots under different potentials.
The electrochemical tests were conducted by a rotating disc electrode (RDE) technique. Cyclic voltammetry (CV), linear sweep voltammetry (LSV) and accelerated durability testing (ADT) were conducted to estimate the electrochemical activity and the durability of the catalysts. The preparation of the catalyst ink, the composition of the three-electrode system and the details of the electrochemical tests refer to our asreported work [45].
Please cite this article as: Wang J et al., Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.054
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analyze the tolerance of single cell under cell reversal condition. MEAs were kept under a reverse current of 0.2 A cm2 with cell temperature of 80 C, relative humidity (RH) of 100%, cathode and anode supplied with air and N2. The voltage-time (V-t) curves of the single cells were recorded when the cell voltages drop from open-circuit voltage to 2.0 V, and then the polarization curves were also measured to evaluate the changes of the single cell performances before and after the cell reversal test.
Result and discussion To find out the effect of adding OER catalyst on the structure and property of the composite catalyst, the physical and electrochemical characterizations were carried out.
Physical characterization of the composite catalyst Fig. 1a and b are TEM images of the composite catalyst consisting of PtNi/C Oct, IrO2 and RuO2. Besides the light gray carbon supports and the dark gray PtNi/C Oct nanocrystals of about 6 nm as shown in the HRTEM image embedded in Fig. 1b, the fine equiaxed IrO2 grains of 3 nm (Fig. 1h) and the larger black RuO2 particles with size range from 20 to 50 nm (Fig. 1i) can be also observed. Fig. 1deg are the EDS mapping images of the composite catalyst, and it exhibits that IrO2 and RuO2 are uniformly dispersed in PtNi/C Oct, and especially IrO2 with smaller size shows a higher dispersion degree, which provides a guarantee for better promoting water oxidation and preventing carbon corrosion. The XRD spectra of the composite catalyst are shown in Fig. 2. The diffraction peaks of (111), (200), (220) and (311) facets of PtNi octahedra appear at 41 , 47 , 69 and 83 , respectively. The larger diffraction angles compared with pure Pt demonstrate the formation of PtNi alloy phase. The sharp diffraction peaks at 28 , 35 and 54 correspond to (110), (101) and (211) facets of IrO2 and RuO2 rutile phase, and their (111) diffraction peaks near 40 are covered by the PtNi(111) peak. Combining the above TEM results, because the diffraction peak positions of IrO2 and RuO2 are similar, the peaks of IrO2 with smaller size are wider and flatter, and the peaks of RuO2 with larger size are sharper. Therefore, the IrO2 peaks are covered, the RuO2 peaks with very small full width at half maximum (FWHM) can be obviously observed on the whole. Fig. 4 e (a) CV curves of the composite catalyst and PtNi/C Oct, (b) the comparison of CV curves of the composite catalyst before and after 2000 cycles ADT, (c) the comparison of ECSA changes of the composite catalyst, PtNi/C Oct and Pt/C (JM) before and after ADT.
Characterization and cell reversal durability test of MEAs All MEAs were performed the same single cell tests as following. The polarization curves were obtained by the steps as reported in our work [45]. Cell reversal test is employed to
Electrochemical characterization of the catalysts Fig. 3a shows the LSV curves of PtNi/C Oct at different rotating speeds. All the four LSV curves are composed of three different regions. When the potential is less than 0.54 V, it is the diffusion control region; when the potential is higher than 0.75 V, it is the dynamic control region; when the potential is between 0.54 V and 0.75 V, it is the mixed control region. The limiting current density of LSV curve in the diffusion control region increases with the increase of the electrode rotating speed. The ORR kinetics of PtNi/C Oct is analyzed by KutkayLewitic (K-L) equation. The K-L plots under different potentials are presented in Fig. 3b, and the average numbers of
Please cite this article as: Wang J et al., Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.054
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Fig. 5 e (a) SEM image of the anode catalyst layer of the MEA fabricated using the composite catalyst and the EDS mapping of (b) Pt, (c) Ni, (d) Ir, (e) Ru.
Fig. 6 e The comparison of performance curves of MEA fabricated with PtNi/C Oct in cathode and the composite catalyst in anode and the controls prepared with only PtNi/ C Oct or Pt/C (JM).
oxygen. Therefore, as mentioned in our previous work [45], the mass activity and specific activity of PtNi/C Oct employed in this work reach 6.1 and 6.6 times of Pt/C (JM), respectively, so its application in the cathode is conducive to better power generation performance of MEA. Fig. 4a shows the CV curves of the composite catalyst and PtNi/C Oct. The calculated electrochemically active surface area (ECSA) of the composite catalyst is 42.1 m2 g1 Pt , which is lower than that of the latter, revealing that the 6.6 m2 g1 Pt surface of PtNi/C Oct crystal still plays a catalytic role in the composite catalyst, but the exposure of active sites is affected by the addition of OER catalyst, so the ECSA of the composite catalyst slightly decreases. Fig. 4b exhibits the change of CV curves of the composite catalyst before and after ADT. After 2000 cycles, its ECSA decreases by 21.4% as shown in Fig. 4c. According the comparison of CV curves of PtNi/C Oct and Pt/C (JM) before and after ADT reported in our previous work [45], the ECSA attenuations
transferred electrons n and the curve slopes 1/B calculated according to the K-L equation are listed in Table 1. Each n value is close to 4, indicating that the ORR on PtNi/C Oct mainly follows the four-electron reaction mechanism. Compared with the two-electron reaction on pure Pt surface, four-electron reaction is more favorable for the reduction of
Table 2 e The comparison of power generation performances of MEAs fabricated using the composite catalyst, PtNi/C Oct and Pt/C (JM). Anode catalyst
PtNi/C Oct þ IrO2 þ RuO2 PtNi/C Oct Pt/C JM
Maximum power density (mW cm2)
Cell voltage @1 A cm2 (V)
923.4
0.672
954.0 804.4
0.679 0.649
Fig. 7 e The comparison of the V-t curves of the MEA prepared using the composite catalyst in anode and the control prepared with only PtNi/C Oct during the process of the cell reversal.
Please cite this article as: Wang J et al., Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.054
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Fig. 8 e The comparison of performance curves of (a) the MEA prepared using the composite catalyst in anode and (b) the control prepared with only PtNi/C Oct before and after the cell reversal test, and the changes of (c) cell voltage at 1 A cm¡2 and (d) maximum power density.
of two controls are 22.8% and 38.9% under the same test conditions, respectively, indicating that the composite catalyst has higher electrochemical stability. In previous work [45], we have investigated the reasons for the activity attenuations of PtNi/C Oct during ADT. It is believed that its degradation should impute to the loss of alloy (111) facets caused by the change of octahedral morphology and the Pt loss owing to the carbon corrosion. The addition of OER catalyst can inhibit the carbon corrosion to a certain extent, so that the durability of the composite catalyst can be improved. According to the above physical characterization results, IrO2 and RuO2 are successfully added into PtNi/C Oct by
physical mixing method and ensure a certain degree of dispersion. The addition of OER catalyst has a certain effect on the electrochemical performance of the composite catalyst, making its initial activity slightly reduced and its electrochemical durability slightly improved.
Power generation performance of the composite catalyst for PEMFC anode To investigate the application potential of the MEA consisting of highly active PtNi/C Oct in cathode and the composite catalyst in anode, its power generation performance in the
Fig. 9 e TEM images of (a) the composite catalyst and (b) PtNi/C Oct in MEA anodes after the cell reversal test. Please cite this article as: Wang J et al., Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.054
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Fig. 10 e SEM images and EDS of the anode catalyst layer of the MEA prepared using the composite catalyst (a, c, e) before and (b, d, f) after the cell reversal test.
actual single cell was tested and compared with the two controls. Fig. 5 is SEM image of the anode in the MEA prepared by the composite catalyst and its EDS mapping images. The surface of the anode is fairly flat before the test, and the four metal elements, Pt, Ni, Ir and Ru are uniformly distributed, demonstrating that PtNi/C Oct and OER catalyst are well-distributed
in the catalyst layer, which will be beneficial to improving the power generation performance of single cell and protecting the carbon supports. Fig. 6 exhibits the performance curves of the three MEAs, and their single cell performance parameters are summarized in Table 2. The cell voltage at 1 A cm2 of MEA fabricated using the composite catalyst reaches 0.672 V and its maximum
Please cite this article as: Wang J et al., Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.054
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power density is 923.4 mW cm2, which are slightly lower than those prepared using only PtNi/C Oct. Its slightly lower power generation performance may be ascribed to the increase of catalyst layer thickness and the changes of hydrophilicity resulted from the addition of OER catalyst. However, its power generation performance still has obvious advantages compared with the control prepared using Pt/C (JM), and its above two parameters are improved by 23 mV and 119 mW cm2, respectively. As mentioned in Section Electrochemical characterization of the catalysts, it is because PtNi/C Oct with enhanced ORR activity can better meet the requirement of the cathode for high catalytic activity.
Cell reversal durability of MEA fabricated with the composite catalyst in anode The cell reversal durability tests of MEA fabricated using the composite catalyst and the control prepared with only PtNi/ C Oct were conducted, and their V-t curves are presented in Fig. 7. Because the anode is supplied with N2 and fuel is insufficient, the control can only provide electrons and protons to the cathode by water electrolysis and carbon oxidation in the anode. The whole process of reducing the cell voltage to 0.2 V only takes about 11 min. For MEA fabricated using the composite catalyst, with the anode potential gradually increasing to water oxidation potential of 1.23 V, electrons and protons are provided to the cathode by the rapid water oxidation in the presence of OER catalyst, which will avoid the corrosion of the carbon supports. Therefore, a relatively flat platform appears in this region of the V-t curve, and the cell voltage does not significantly decrease. At this stage, the anode potential is as high as 1.5 Ve1.7 V, and the increase of the anode potential causes that the cell voltage decreases from 0.6 V to 0.8 V. As the rate of water oxidation can no longer meet the need of the cathode reaction, the carbon corrosion begins to occur significantly. The cell voltage continues to decrease from 0.8 V and the slope of the V-t curve gradually increases until the cell voltage drops to 2.0 V. The whole cell reversal test lasts 71 min. Fig. 8 compares the power generation performance of the two MEAs before and after the cell reversal test. After tests, their cell voltages at 1 A cm2 and maximum power densities obviously decline. For the one fabricated using the composite catalyst, above two parameters decrease by 104 mV and 266.8 mW cm2, and the attenuation rates are 15.5% and 28.9%, respectively. For the control, they decrease by 135 mV and 335.2 mW cm2 with the attenuation rates of 19.9% and 35.1%, respectively, indicating that the performance degradation of the MEA prepared with the composite catalyst is still lower, although the cell reversal process is prolonged by 1 h, which also demonstrates that the application of the composite catalyst in the anode can improve the cell reversal resistance of the single cell. Fig. 9 show TEM images of the anode catalysts in the two MEAs after the cell reversal test. In the right image, light gray spherical carbon particles can be hardly observed, and serious carbon corrosion causes more obvious agglomeration of nanocrystals. In the left image, the carbon particles can still be
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observed, indicating that the addition of OER catalyst slows down the corrosion of the carbon supports, so the performance retention rate of MEA fabricated using the composite catalyst is higher after test. The SEM and EDS images of the MEA anode fabricated with the composite catalyst before and after the cell reversal test are presented in Fig. 10. After test, the surface of the anode catalyst layer becomes rough and many pits caused by the carbon corrosion appear. Because the thickness of the catalyst layer should be greater than the detection depth of EDS, all fluorine element comes from the ionomer Nafion added to the catalyst slurry. According to the EDS results shown in Fig. 10e and f, it can be found that the C and Pt contents relative to F significantly decrease after the cell reversal test, demonstrating that the corrosion of the carbon supports and the loss of the active components occur. It indicates that the carbon corrosion is still unavoidable during such a long cell reversal process despite adding OER catalyst. However, during the actual vehicle driving process, the insufficient fuel supply can be usually found in time, so the cell reversal generally occurs instantaneously and lasts very short. Therefore, the addition of OER catalyst such as IrO2 and RuO2 can still effectively inhibit the irreversible damage caused by the cell reversal. Combining above results of the single cell test, it can be proved that the MEA fabricated with highly active PtNi/C Oct in the cathode and the composite catalyst in the anode obviously improves the power generation performance and cell reversal resistance of the single cell.
Conclusion In this work, the MEA with both enhanced power generation performance and good cell reversal durability is successfully prepared using highly active PtNi/C Oct in the cathode and the composite catalyst containing PtNi/C Oct and OER catalyst in the anode. Its power generation performance is higher than the control fabricated with Pt/C (JM), and the cell voltage at 1 A cm2 and the maximum power density are increased by 23 mV and 119 mW cm2. Especially the holding time of MEA fabricated with the composite catalyst is prolonged by 1 h under continuous cell reversal condition, and its performance retention rate after test is also higher, revealing that the cell reversal tolerance of MEA is effectively improved. These results demonstrate that this work not only achieves the actual single cell application of the octahedral catalyst, but also effectively reduces the damage caused by the cell reversal while ensuring good power generation performance. This work has a certain practical significance to promote the commercialization of PEMFC.
Acknowledgement The authors appreciate the National Natural Science Foundation of China (No.21676204).
Please cite this article as: Wang J et al., Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.054
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Please cite this article as: Wang J et al., Highly efficient, cell reversal resistant PEMFC based on PtNi/C octahedral and OER composite catalyst, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2020.01.054