NiCo2O4-based wool-ball as an electrocatalyst for methanol assisted water splitting, an alternative to water splitting

Abstract

Hydrogen energy is considered a potential solution to the energy crisis and environmental pollution concerns. Pure hydrogen can be produced from electrochemical water splitting, however, the oxygen evolution reaction (OER) is the primary obstacle due to its sluggish reaction kinetics. Introducing methanol oxidation is one possible solution to replace OER for water splitting to produce hydrogen as an energy source. In this article, a NiCo₂O₄-based wool-ball electrocatalyst was prepared via a solvothermal process followed by annealing. The catalyst showed high purity and a wool-ball structure, where the threads are arranged in different patterns and composed of sub-nano-sized spheres. The catalyst exhibited an excellent response to oxidation reactions and reduced severely the potential for 250 mV, when 1.17 mM of methanol was introduced into a 1 M KOH solution. The catalyst also demonstrated good performance for the hydrogen evolution reaction (HER), however, there was a reduction in performance in the presence of methanol. This might be due to the formation of a methanol layer that inhibits the HER in the KOH solution, as methanol does not participate in HER. This resistance was confirmed with electrochemical impedance spectroscopy (EIS) and electrochemical surface area (ECSA) measurements, where the ECSA value in KOH was 4.10, which reduced to 2.63 in the presence of methanol. The catalyst exhibited excellent stability for both HER and methanol oxidation reaction (MOR) over a long duration of 3600 s. • The NiCo 2 O 4 reduce the overpotential for 240 mV. • NiCo 2 O 4 based wool-ball are prepared via solvothermal follow by annealing method. • The catalyst showed excellent stability for 3600 s and high ECSA of 12.88 mF/cm 2 . • The catalyst follow Volmer-Heyrovsky mechanism as per Tafel slope.

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