Advanced Cathode Electrocatalysts for Fuel Cells: Understanding, Construction, and Application of Carbon-Based and Platinum-Based Nanomaterials

Proton-exchange-membrane fuel cells (PEMFCs) are one type of promising energy device with clean and high efficiency characteristics. The sluggish kinetic characteristics of cathode oxygen reduction reaction (ORR) are still the bottleneck of the crucial skill. Until now, the exploitation of high ORR performance nanocatalysts has been the most effective strategy to the commercial of PEMFCs. Hence, more attention is paid to preciously tuning the surface/interface electronic structure and optimizing the intermediate species of adsorption energy of nanocatalysts to improve the ORR performance. Herein, performance-construction engineering is introduced in terms of surface strain, defect site (adsorption site/coordination number effect), and crystal facet for Pt-based catalysts. The physical synergy between Pt-based and carbon-based catalysts is also systematically reported focusing on ordered and mesoporous carbon, physical encapsulated carbon, metal carbides, carbon-containing polymer, etc. for ORR mainly in acidic environment. The understanding, construction, and application of the ORR active sites combined the carbon-based and platinum-based catalysts are deeply concluded in low-temperature PEMFCs, as well as part of high-temperature PEMFCs under acidic environment. The doping strategy and the strong interaction are highlighted introduced to enhance the intrinsic activity and the apparent activity. Furthermore, to study the complex active sites of catalysts and the corresponding compositional and structural evolution, the structure–activity relationships are further depicted coupled with the existing advanced in situ characterization technology. Finally, the potential prospects and challenges for the two types of electrocatalysts are summarized to shed a new light for the development of ORR catalysts in commercial applications.