Recently, a research achievement entitledGraphene-Nanopocket-Encaged PtCo Nanocatalysts for Highly Durable Fuel Cell Operation under Demanding Ultralow-Pt-Loading Conditionsis published in Nature Nanotechnology, which is mainly completed by Prof. Zhao Zipeng of BIT and Prof. Huang Yu of UCLA.

This research reports a graphene-nanopocket-encaged PtCo nanocatalysts and its application to proton exchange membrane fuel cells (PEMFCs) as cathode catalysts, so that the power density and durability of fuel cell can reach the international advanced level at the same time under extremely challenging conditions ultralow-Pt-loading. It is expected that this reported catalyst can reduce the amount of Pt group metals (PGM) required for fuel cell vehicles to a level equivalent to that required for exhaust gas treatment of internal combustion engine vehicles, which means significantly reducing the amount of PGM required for fuel cells, greatly lowing the costs in large-scale production, and making its large-scale application no longer limited by the extremely limited reserves and output of PGM, paving the way for further promoting the large-scale application of fuel cells. This research will be a key step in the large-scale promotion of PEMFCs and an important breakthrough in this field.

PEMFCs, as green power device that can replace internal combustion engines, can theoretically not rely on carbon containing fossil energy. Therefore, the development and application of PEMFCs is of great significance to achieve the national development goals of “emission peak” and “carbon neutrality”. For the current commercial PEMFCs, PGM are irreplaceable catalyst materials, especially for accelerating the slow oxygen reduction reaction (ORR) of the cathode. PGM are also also required for internal combustion engine vehicles and for catalytic exhaust gas treatment. At present, the demand of the automotive industry accounts for nearly half of the global output of PGM, and the current demand for PGM for fuel cell vehicles is 5-10 times that of internal combustion engine vehicles. With the current demand for PGM for fuel cells, the replacement of internal combustion engine vehicles by fuel cell vehicles will inevitably lead to a shortage of PGM. Due to the extremely limited reserves and output of PGM in the world, this is a great obstacle to the large-scale application of fuel cells. In addition, according to estimates of the U.S. Department of Energy, PGM will be the main cost (accounting for about 40% of the total cost) after the large-scale production of fuel cells. Therefore, reducing the consumption of PGM in commercial fuel cells without compromising performance is crucial for the large-scale application of fuel cells, and also contributes to to the early realization of “carbon neutrality”. However, in the previous application scenarios, the reduction of PGM loading often brings about the sacrifice of fuel cell device performance and poor stability, which makes scientific researchers all over the world compete to develop catalysts with higher catalytic activity and more stability, so as to reduce the demand for PGM in fuel cell vehicles to the level of internal combustion engine vehicles.

The research team has designed and synthesized an ultrafine graphene-nanopocket-encaged PtCo nanocatalysts (Fig. 1), through which, the ultrafine nanocatalyst is protected in the graphene-nanopocket, not only ensuring the electrochemical activity, but also limiting the aggregation of the catalyst, and alleviating the oxidation dissolution and Ostwald ripening process of the catalyst. This special structure can still ensure excellent activity and stability even under very harsh ultra-low PGM loading. The catalyst obtained is applied to the fuel cell membrane electrode assembly (MEA), and its comprehensive performance as a cathode catalyst is one of the best catalysts that give consideration to quality, activity and stability (Fig. 2). The mass-normalized rated power of the MEA using PtCo@Gnp can reach 13.2 WmgPGM-1, and the durability has reached the international advanced level (Fig. 3), which is expected to convert the PGM required for a 90 kW fuel cell vehicle. It is significantly reduced to around 6.8 grams, which is close to the level of pgm consumption required for internal combustion engine vehicles. Compared with the commercial Pt/C and c-PtCo/C catalysts, the excellent stability of PtCo@Gnp is mainly due to its retention of the nanocatalyst particle size (Fig. 4).

Fig. 1 Schematic diagram of nanopocket-encaged design and characterization of PtCo@Gnp

Fig. 2 Comparison of MEA performance of Pt/C, c-PtCo/C and PtCo@Gnp catalysts with representative catalysts in the literature

Fig. 3 MEA polarization curves at ultra-low PGM loadings (cathode and anode total of 0.07 mgPGMcm-2) tested in a hydrogen/air environment

Fig. 4 Catalyst characterization, particle size distribution analysis and corresponding MEA test results after accelerated aging test

Paper link: https://www.nature.com/articles/s41565-022-01170-9

Paper DOI: https://doi.org/10.1038/s41565-022-01170-9

About the author:

Prof. Zhao Zipeng, doctoral supervisor of School of Materials Science and Engineering, BIT, has long been engaged in hydrogen energy related catalysis research, including electrolytic water devices and fuel cells. His research involves the creation of new catalysts, macro preparation, and application to MEA and stacks, and he has published over 50, with a total of more than 11000 citations, and has won the UCLA Postdoctoral Research Chancellor’s Award.