Facilitating active NiOOH formation via Mo doping towards high-efficiency oxygen evolution

Abstract

The insufficient performance of non-noble metal catalysts in alkaline media is a prominent issue that limits the widespread adoption of electrocatalytic water splitting. In this study, we present an efficient Mo doping strategy to boost the electrocatalytic performance of NiFe layered double hydroxide (LDH) through modulating the electronic structure of active Ni sites. The optimized Mo doped NiFe-LDH (denoted as NiFeMo-2) exhibits significantly improved activity, showing a smaller overpotential of 262 mV at 10 mA cm⁻² compared to NiFe-LDH (344 mV). X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) spectra demonstrate that the incorporation of Mo not only increases the electron cloud density of Ni, but also induces more oxygen vacancies. Due to these structural modifications, the oxygen evolution reaction (OER) kinetics is dramatically enhanced, confirmed by in situ electrochemical impedance spectroscopy (EIS). Moreover, in situ Raman spectroscopy shows that the Mo doping can facilitate the formation of active NiOOH species at a lower potential, thus accelerating the OER kinetics. The in situ differential electrochemical mass spectrometry (DEMS) technique with ¹⁸O isotope labelling, tetraalkylammonium cation (TMA⁺) chemical probe, and ethanol oxidation reaction suggest that the NiFeMo-LDH catalyst primarily follows the adsorbate evolution mechanism (AEM) pathway, the promoted dehydrogenation process with the modulation of *OH adsorption. This study reports a high-performance non-noble metal OER electrocatalyst and unveils the origins of metal doping to enhance the OER kinetics.