Effective alkaline water electrolysis on nwMnO2-nsNi(OH)2 composite electrode via lattice oxygen participant adsorbate evolving mechanism

Abstract

To improve and maintain the oxygen evolution reaction (OER) performance of MnO2 in water electrolysis for a long time, this study attempts to utilize Ni(OH)2 nanosheets (ns), which have excellent electrochemical properties. Nanocomposites of MnO₂ and Ni(OH)2 were directly grown on a carbon paper (CP) electrode using hydrothermal synthesis. The MnO2 nanowires (nw) appeared to be wrapped by the Ni(OH)2 nanosheets in the MnO2-Ni(OH)2 composites. The MnO2-Ni(OH)2 composite electrode exhibited better OER performance than the nwMnO2@CP or nsNi(OH)2@CP electrodes. In particular, in a 1.0 M KOH alkaline electrolyte, the 1.0 nwMnO2-1.0 nsNi(OH)2@CP electrode showed the highest OER performance with a cell potential of 1.64 V and Tafel slope of 68 mV dec−1 at a 10 mA cm−2 of current density (η = 0.41 V). The X-ray photoelectron spectroscopy of nwMnO2-nsNi(OH)2@CP before and after the OER revealed the formation of more oxygen vacancies, which served as OH-adsorption sites, leading to higher OER activity. The stability of the 1.0 nwMnO2-1.0 nsNi(OH)2@CP electrode was demonstrated through 300 h-OER long-term tests, which yielded a high Faradaic efficiency of 96.2%. The lattice oxygen transfer plays a significant role in enhancing the intrinsic activity of catalysts during OER. The synergy between nwMnO2 and nsNi(OH)2 accompanies a lattice oxygen participant adsorbate evolving mechanism.