Iridium (Ir)-based catalysts are highly efficient for the anodic oxygen evolution reaction (OER) due to high stability and anti-corrosion ability in the strong acid electrolyte. Recently, intensive attention has been directed to novel, efficient, and low-cost Ir-based catalysts to overcome the challenges of their application in the water electrolysis technique. To make a comprehensive understanding of the recently developed Ir-based catalysts and their catalytic properties, the mechanism and catalytic promotion principles of Ir-based catalysts were discussed for OER in the acid condition aimed for the proton exchange membrane water electrolyzer (PEMWE) in this review. The OER catalytic mechanisms of the adsorbate evolution mechanism and the lattice oxygen mechanism were first presented and discussed for easy understanding of the catalytic mechanism; a brief perspective analysis of promotion principles from the aspects of geometric effect, electronic effect, synergistic effect, defect engineering, support effect was concluded. Then, the latest progress and the practical application of Ir-based catalysts were introduced in detail, which was classified into the varied composition of Ir catalyst in terms of alloys, hetero-element doping, perovskite, pyrochlore, heterostructure, core–shell structure, and supported catalysts. Finally, the problems and challenges faced by the current Ir-based catalyst in the acidic electrolyte were put forward. It is concluded that highly efficient catalysts with low Ir loading should be developed in the future, and attention should be paid to probing the structural and performance correlation, and their application in real PEMWE devices. Hopefully, the current effort can be helpful in the catalysis mechanism understanding of Ir-based catalysts for OER, and instructive to the novel efficient catalysts design and fabrication.

Methanol electrolysis is significant but challenging as an energy-saving technique for electrochemical hydrogen production. Herein, we demonstrated a novel and efficient bifunctional catalyst of CoSe/N-doped carbon nanospheres supported Pt nanoparticles for hydrogen generation via methanol electrolysis; high catalytic performance for both methanol oxidation (MOR) and hydrogen evolution (HER) was observed benefitting from the effective interaction of metal and support effect as well as the oxophilic characteristics of cobalt selenide. Theoretical calculation disclosed the increased charge density of Pt induced by the CoSe/NC support has a bifunctional ability for optimizing the H* adsorption energy for hydrogen evolution reaction and weakening the CO adsorption energy of methanol oxidation reaction. Specifically, the largely improved CO-tolerance ability was observed in the CO-stripping technique, where about 90 mV less of the peak potential for CO oxidation than that of Pt/C catalyst was observed, resulting from a strong electronic effect as indicated by the spectroscopic analysis. The peak current density of 84.2 mA·cm^–2 was found for MOR, which was about 3.1 times higher than that of Pt/C; and a low overpotential of 32 mV was required to reach 10 mA·cm^–2 for HER in 0.5 mol·L^–1 H₂SO₄ with 1.0 mol·L^–1 CH₃OH. When serviced as both anode and cathode catalyst in a methanol electrolyzer, a low cell potential of 0.67 V to offer 10 mA cm^-2 was obtained, about 170 mV less than that of Pt/C catalyst; moreover, it was 1.1 V lower than that of water-splitting (1.77 V), indicating a promising energy-saving technique for hydrogen generation. They also showed very good catalytic stability and anti-poisoning ability during the catalysis process. This work would help understand the metal-support interaction for hydrogen generation vis methanol electrolysis.

Transition metal phosphide (TMP), as an ideal catalytic promoter in methanol fuel oxidation, has received increased attention because of its multifunctional active sites, tunable structure and composition, as well as unique physical and chemical properties and efficient multi-composition synergistic effect. Some advances have been made for this catalyst system recently. In the current review, the research progresses of transition metal phosphides (TMPs) in the assisted electrooxidation of methanol including the catalysts fabrication and their performance evaluation for methanol oxidation are reviewed. The promotion effect of TMPs has been firstly presented and the catalyst systems based on the different metal centers of TMPs are then mainly discussed. It is concluded that the TMPs can greatly promote methanol oxidation through the electronic effect and the oxyphilic property based on the bifunctional catalytic mechanism. The problems and challenges in methanol fuel oxidation by using TMPs are also described at the end with the attention being paid to the precise catalyst design. The catalytic mechanism probing and application of the fuel cells device are proposed. The current effort might be helpful to the community for novel catalyst system design and fabrication.

The low intrinsic activity of Fe/N/C oxygen catalysts restricts their commercial application in the fuel cells technique; herein, we demonstrated the interface engineering of plasmonic induced Fe/N/C-F catalyst with primarily enhanced oxygen reduction performance for fuel cells applications. The strong interaction between F and Fe-N₄ active sites modifies the catalyst interfacial properties as revealed by X-ray absorption structure spectrum and density functional theory calculations, which changes the electronic structure of Fe-N active site resulting from more atoms around the active site participating in the reaction as well as super-hydrophobicity from C–F covalent bond. The hybrid contribution from active sites and carbon support is proposed to optimize the three-phase microenvironment efficiently in the catalysis electrode, thereby facilitating efficient oxygen reduction performance. High catalytic performance for oxygen reduction and fuel cells practical application catalyzed by Fe/N/C-F catalyst is thus verified, which offers a novel catalyst system for fuel cells technique.