High ratios of Ni3+ and Co3+ facilitated by Mn-addition for enhanced oxygen evolution reaction and ethanol oxidation reaction

Abstract

The design of dual-functional catalysts for the oxygen evolution reaction and ethanol oxidation reaction is essential for improving hydrogen production efficiency, and one of the strategies to improve catalytic performance is the incorporation of high-valence metals. However, the generation of high-valence metals has always been a challenge in the field of catalysis, and elucidating the involved mechanisms is also difficult. Herein, we synthesized a metal–organic framework (MOF) material on nickel foam (NF) using a straightforward one-step hydrothermal technique and subsequently transformed it into a metal oxide hydroxide through activation, denoted as Co₁Ni_0.5Mn₁BDC@NF-A. The catalyst with Mn enhanced exhibits a curved sheet-like morphology, arranged in an ordered layered structure, with abundant active surfaces. Mn induces additional production of Ni³⁺ and Co³⁺ to accelerate the OER/EOR process. The catalyst exhibits outstanding electrochemical performance in both the OER, with an overpotential of 298 mV at 100 mA cm⁻², and the EOR, with a potential of 1.30 V at 100 mA cm⁻², demonstrating superior performance compared to other Ni-based and Co-based catalysts. Furthermore, to reach 100 mA cm⁻², the combined EOR–HER process requires only 1.39 V, while the combined OER–HER process requires just 1.54 V. The remarkable performance is attributed to the inclusion of Mn, which can promote the transformation of morphology, mainly transforming the catalyst from disordered stacking to an ordered staggered arrangement, exposing more active sites. More importantly, XPS testing shows that Mn reduces the binding energy of the Ni/Co(II) to Ni/Co(III) transition by adjusting the hybridization effect between Ni 3d, Co 3d and O 2p orbitals, promoting the generation of Ni³⁺ and Co³⁺ for enhanced reaction kinetics. In summary, this work presents a simple yet effective strategy for the generation of high-valence transition metals, which can be used to accelerate the OER and EOR processes, thus offering promising prospects for advancing hydrogen production technology.