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

Abstract

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