Enhancing the Hydrogen Evolution Activity of Ni-Based Electrocatalysts Through Codoping of Chromium and Molybdenum

Abstract Electrochemical water splitting represents an alternative method for producing molecular hydrogen, a promising clean energy alternative to fossil fuels. Ni-based alloys have received increased attention as earth-abundant catalysts for the hydrogen evolution reaction (HER), where performance can be optimized through alloying with heteroatoms. Herein, we report an integrated theoretical and experimental study that elucidates the effects of Cr and Mo doping on the HER activity and stability of Ni1–xCrx, Ni1–yMoy, and Ni1–x–yCrxMoy alloy nanocrystals (NCs). Theoretical calculations predicted that codoping of Cr/Mo can significantly enhance the HER activity of Ni, as evidenced by more favorable hydrogen binding free energies (|ΔGH|) achieved for Ni1–x–yCrxMoy alloys. Accordingly, a series of binary and ternary alloys were colloidally synthesized to investigate the composition-dependent HER activity in alkaline electrolytes. Morphological analysis of Ni1–xCrx and Ni1–yMoy NCs revealed average sizes of 10.2 ± 2.0 and 13.4 ± 2.8 nm, respectively while Ni1–x–yCrxMoy alloys showed significantly larger (33.3 ± 8.9 – 37.4 ± 17.6 nm) diameters. Nonetheless, the cubic structure of parent Ni NCs was retained upon codoping of Cr/Mo. Surface analysis revealed prominent variations in surface chemistry, leading to a shift of electron density from Ni toward Cr and Mo. HER performance revealed a volcano trend in electrocatalytic activity with Ni0.914Cr0.057Mo0.029 composition displaying the highest activity, which is comparable to Pt/C standard (10% wt) at a current density (j) of –10 mA/cm2. Despite all alloys displaying Volmer-influenced HER kinetics, simultaneous admixing of 5.7% Cr and 2.9% Mo produced the lowest Tafel slope (80 mV/dec), suggesting enhanced catalytic activity for the optimally doped composition. The codoping of Cr/Mo substantially improved the charge transfer resistance, electrochemically active surface area, and short-term stability of alloys in alkali. This study advances our understanding of the composition-dependent HER activity of Ni-based alloys and demonstrates how computationally guided doping strategies can be utilized to produce high-efficiency and earth-abundant catalysts for water electrolysis.