The metal-support interaction effect in the carbon-free PEMFC cathode catalysts

Proton exchange membrane fuel cells (PEMFCs) have been regarded as an effective means to transform hydrogen energy into electric energy, which is featured with high energy density, excellent conversion efficiency, and environmental friendliness. Carbon nanomaterials are the most widely used supports for the state-of-the-art Pt-based PEMFC cathode catalysts. Nonetheless, the corrosion of carbon supports under high potential environment would inevitably lead to the dissolution/ripening of Pt, resulting in the severe degradation of their PEMFC performance. Carbon-free materials, such as transition metal oxides/nitrides/sulfides/carbides (TMOs, TMNs, TMSs, and TMCs), can effectively prevent this issue with their excellent intrinsic stability and tuned metal-support interactions (MSI). Recently, numerous researches have been focused on the design and preparation of carbon-free PEMFC cathode catalysts. Meanwhile, MSI effect, including d-band center, migration energy barrier, defect sites, coordination environment, and electron transfer ability, have also been considered to improve the PEMFCs performance. In this review, the MSI effect of carbon-free PEMFC cathode materials and their common adjustment strategies are systematically summarized. Then, details about the pristine and modified carbon-free PEMFC catalysts and their specific structure-activity relationships induced by MSI effect are further illustrated in the order of TMOs, TMCs, TMNs, and TMSs. Finally, the challenges and perspectives of carbon-free PEMFC cathode catalysts are further proposed to provide insights into future researches in this PEMFC field.