Synergistic electronic tuning and active site optimization in bimetallic Pt-Pd-Doped ZnCo₂O₄ spinel nanoelectrocatalyst for boosted electrocatalytic green hydrogen evolution supported by DFT

Abstract

In this in-depth study, we developed a series of electrocatalysts by doping platinum (Pt) and palladium (Pd) into the zinc cobaltite system, yielding $\mathrm{Zn}{\mathrm{Pt}}_x{\mathrm{Pd}}_x{\mathrm{Co}}_{2-2x}{O}_4@\mathrm{NF}\left(0\le x\le 0.08\right)$ nanoelectrocatalyst. The noble metals Pt and Pd were introduced in controlled, low concentrations (< 8 %) to optimize the catalytic performance. The electrocatalysts were synthesized directly on nickel foam (NF) using an in situ hydrothermal method. Comprehensive characterization, including XRD, SEM, TEM, HR-TEM, EDX, and XPS, confirmed the cubic spinel oxide structure, morphology, and chemical composition of the catalysts. The optimized catalyst (x = 0.08) exhibited an impressive overpotential of 55 mV at −10 mA/cm², accompanied by a Tafel slope of 23 mV/dec. Density functional theory (DFT) calculations revealed that co-doping $\mathrm{Zn}{\mathrm{Co}}_2{O}_4$ with Pt and Pd enhances hydrogen evolution reaction (HER) activity through modification of the electronic structure, reduction of water dissociation barriers, and facilitation of synergistic adsorption across active sites. Specifically, while Pt sites exhibit strong $H^{\ast }$ adsorption ($∆G_{H^{\ast }}$ = −0.522 eV), this is counterbalanced by the nearly thermoneutral adsorption at adjacent O sites ($∆G_{H^{\ast }}$ = −0.106 eV), resulting in a synergistic effect that mitigates potential active site poisoning on $\mathrm{Zn}{\mathrm{Pt}}_x{\mathrm{Pd}}_x{\mathrm{Co}}_{2-2x}{O}_4$. This complementary interaction enables sustained hydrogen production by balancing adsorption strengths across the catalyst surface. The presence of Pd and Co further contributes to this moderation, supporting efficient HER kinetics. These findings establish bimetallic doping as a promising strategy for optimizing electrocatalysts for green hydrogen production.