Comprehensive insights into hydrolysis-mediated hydrogen production using high-entropy quintuple alloy-grafted carbon black

Abstract

Hydrogen is a promising fuel with adequate energy density and zero carbon emissions upon combustion. Its fast and convenient production from hydrogen-rich materials like sodium borohydride (NaBH₄) is of high practical importance. Herein, we report a novel quintuple high-entropy alloy of CrMnFeCoNi loaded on conductive carbon (HEACB) as an effective heterogeneous catalyst for the hydrolysis of NaBH₄ to produce hydrogen at room temperature. The optimized HEACB shows excellent performance with a turn over freequency (TOF) of about 188 mL g_Mn⁻¹ s⁻¹ and a minimum activation energy (E_a) of about 15 kJ mol⁻¹, while the E_a of bare HEA is 43 kJ mol⁻¹. Mott–Schottky analysis reveals n-type semiconductor behavior of the HEACB heterostructure at the electrolyte interface during the reaction with an optimal flat band potential. Electrochemical analysis is employed to understand the kinetic aspects of the observed catalytic behavior during hydrolysis. The onset potential, overpotential, Tafel slope, and charge transfer resistance extracted from linear sweep voltammetry and electrochemical impedance studies reveal that the HEA alloy stabilization greatly affects the overall catalytic efficiency towards NaBH₄ hydrolysis. Chemical and electrochemical investigations exhibit a pronounced correlation. Density Functional Theory (DFT) is applied to understand the interaction of the reaction intermediates and to provide insights into the hydrolysis process of borohydride on the HEA system.