Molybdenum-doping to enhance the deprotonation ability of nickel-based hydroxide electrocatalysts for ethanol oxidation

Abstract

With technological advancements, the practical application of ethanol oxidation reaction (EOR) is becoming increasingly promising, yet the need for higher ethanol concentrations highlights the growing importance of the deprotonation ability (Ni²⁺ to Ni³⁺) of the catalyst. The deprotonation ability is the key step for nickel-based catalysts in EOR, as it is essential for Ni²⁺ to continuously undergo deprotonation to transform into Ni³⁺ in order to maintain the continuous EOR. Herein, we developed Mo-doped Ni(OH)₂ nanosheets by a hydrothermal method. The Mo-doped Ni(OH)₂ nanosheets show excellent EOR performance due to the high valence doping of Mo, the onset potential of the oxidation peak (Ni²⁺ to Ni³⁺) appears at a position with a small overpotential,. The in-situ Raman spectroscopy technique further characterized the increase in NiOOH in the process of EOR. The Mo-doped Ni(OH)₂ nanocomposite catalyst facilitates the oxidation of Ni²⁺ into Ni³⁺. Based on the above theoretical guidance, Mo-doped Fe/Ni(OH)₂ nanosheets was designed and synthesized. The outstanding EOR performance of the Mo-Fe/Ni(OH)₂-3 showed a potential of 1.352 V at 10 mA cm⁻². The catalyst was used to design three-electrode reversible zinc-ethanol-air battery (T-RZEAB), which effectively overcomes the opposing kinetic and thermodynamic requirements for EOR and oxygen reduction reaction (ORR) catalysts in the oxygen electrode. The charging voltage of T-RZEAB with Mo-Fe/Ni(OH)₂-3 is 240 mV lower than that of a traditional zinc-air battery at 25 mA cm⁻².