Unveiling the potential of rock-salt type high entropy oxides synthesized by green microwave irradiation method for excellent oxygen evolution reaction

In recent years high entropy oxides (HEOs) are regarded as appealing candidates for oxygen evolution reaction (OER) due to their unique structural design, excellent functional landscapes, outstanding electrocatalytic activities and superior stability. High OER activity of HEOs is attributed to high active site density, low overpotential and high entropic stabilization effect. Herein, we propose an ultrafast and high-efficiency microwave assisted synthesis route to fabricate HEOs nano-catalysts with five metal elements (Al, Fe, Cu, Ni, Co) and tailor the component ratio to enhance the electrocatalytic performance. Physical characterizations confirmed the phase purity, homogeneous distribution and chemical stability of all HEO compositions. Electrochemical investigations inferred that HEO with 30 % wt. of Fe and Ni showed excellent OER activities among all compositions with low overpotential (eta) of 363 mV and 333 mV, small Tafel slope of 47.7 mVdec- 1 and 45.1 mVdec- 1 at 10 mAcm-2 current density, respectively. All prepared HEOs demonstrated better OER performance and long-time stability over 4 h of electrochemical investigations. This excellent performance of HEOs towards OER is attributed to the high concentration of oxygen vacancies on the material surface and synergistic effect due to multicomponent cointeractions. Our findings emphasize the possibility of synthesizing HEOs with similar crystal structures but varying cation ratios, which leads to lattice distortion and electronic charge imbalance for creation of oxygen vacancies. We believe this finding will broaden the applications of HEO catalysts for viable energy storage (batteries) and conversion (fuel cells) devices.