Synergism of tiny Ni clusters and Pt nanoparticles promoting efficient and stable electrocatalytic methanol oxidation and hydrogen evolution by water electrolysis

Abstract

Herein, we prepared a catalyst composed of tiny Ni clusters (Ni_cs) coexisting with Pt nanoparticles (Pt_NPs), denoted as Pt₁₀/Ni-ZrO₂-NC (NC refers to nitrogen-doped carbon). A porphyrin-based metal–organic framework (PCN-222(Ni)) was synthesized and then subjected to high-temperature pyrolysis to yield Ni-ZrO₂-NC (containing tiny Ni_cs). Subsequently, Pt_NPs were deposited on Ni-ZrO₂-NC by NaBH₄-mediated chemical reduction. The presence of Nics reduces the electron density of Pt_NPs, thereby enhancing electron transfer between Pt_NPs and the support. As a result, Pt₁₀/Ni-ZrO₂-NC exhibits markedly improved performance in both hydrogen evolution (HER: 57.5 mV at 100 mA cm⁻²; MOR: mass activity of 5.31 A mg_Pt⁻¹) compared with Pt₁₀/ZrO₂-NC (HER: 91.7 mV at 100 mA cm⁻²; MOR: MA-3.33 A mg_Pt⁻¹). Ni_cs provide additional active sites for water dissociation due to the oxophilicity of Ni, thus accelerating H–OH bond cleavage and promoting the transfer of H_ads to adjacent Pt_NPs, which subsequently form H₂. In the MOR, Ni_cs similarly act as extra sites for OH* adsorption to facilitate CO_ads removal, thereby enhancing both the activity and stability of the catalyst. CO stripping experiments further reveal that Pt₁₀/Ni-ZrO₂-NC oxidizes CO at lower potentials, demonstrating its excellent CO tolerance. In a two-electrode electrolytic cell, Pt₁₀/Ni-ZrO₂-NC applied to a MOR–HER system [(Pt₁₀/Ni-ZrO₂-NC) MOR∥HER (Pt₁₀/Ni-ZrO₂-NC)] achieves a current density of 50 mA cm⁻² and a cell voltage of only 0.846 V—substantially lower than that required for ([(Pt₁₀/Ni-ZrO₂-NC) OER∥HER (Pt₁₀/Ni-ZrO₂-NC)], 1.435 V) or ([(IrO₂) OER∥HER (Pt/C-JM)], 1.720 V).