Tuning the oxygen-containing microenvironment of the Pt-Ni hetero-interface to accelerate alkaline hydrogen oxidation

Heterojunction electrocatalysts composed of platinum and non-platinum group Ni metals have shown remarkable reactivity and economic advantages during the sluggish hydrogen oxidation reaction (HOR) in alkaline exchange membrane fuel cells (AEMFCs). However, little attention has been paid to the effect of the oxygen-containing microenvironment of the heterogeneous interface on the performance of HOR. Herein, Pt-Ni metallic heterostructures loaded on carbon nanotubes with different oxygen-containing microenvironments were controllably synthesized (Pt-Ni/CNT-x, where x represents different oxygen contents) through a galvanic replacement-annealing reduction-metal oxidation process, exhibiting remarkable alkaline HOR performance. Among them, the electrocatalyst Pt-Ni/CNT-p with an appropriate oxygen content exhibited a mass-specific kinetic current and exchange current density of 881.1 A g_Pt⁻¹ (at an overpotential of 50 mV) and 2.12 mA cm⁻², respectively, not only outperforming its Pt/C counterpart but also making it among the best reported Ni-based HOR electrocatalysts to date. Furthermore, this electrocatalyst exhibited negligible activity decay during long-term electrolysis and good CO tolerance capability. (Semi)quantitative analyses verified that the elevation of intrinsic activities for HOR was closely correlated with the oxygen-containing microenvironment of the Pt-Ni hetero-interface. Further experiments and theoretical calculations indicated that the slightly oxidized heterogeneous interface weakens the adsorption energy of the OH* intermediates, which can thus easily combine with H* species to form H₂O. On the contrary, an excessively oxidized heterogeneous interface will strengthen the adsorption of OH* and thus increase the reaction energy barrier of the above crucial Volmer step. This study not only promotes the development of alkaline HOR heterojunction electrocatalysts, but also provides a scheme to explore the influence of the microenvironment on their catalytic activity.