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Oxygen evolution reaction is a momentous part of electrochemical energy storage and conversion devices such as rechargeable metal–air batteries. It is particularly urgent to develop low-cost and efficient electrocatalysts for oxygen evolution reactions. As a potential substitute for noble metal electrocatalysts, transition metal selenides still prove challenging in improving the activity of oxygen evolution reaction and research into reaction intermediates. In this study, a simple one-step solvothermal method was used to prepare a polymetallic compound carbon matrix composite (Co9Se8/Ni3Se4/Fe3O4@C) with a multilayered nanosheets structure. It exhibited good OER activity in an alkaline electrolyte solution, with an overpotential of 268 mV at 10 mA/cm2. In addition, this catalyst also showed excellent performance in the 24 h stability test. The composite presents a multi-layer sheet structure, which effectively improves the contact between the active site and the electrolyte. The selenide formed by Ni and Co has a synergistic effect, and Fe3O4 and Co9Se8 form a heterojunction structure which can effectively improve the reaction activity by initiating the electronic coupling effect through the interface modification. In addition, carbon quantum dots have rich heteroatoms and electron transferability, which improves the electrochemical properties of the composites. This work provides a new strategy for the preparation of highly efficient OER electrocatalysts utilizing the multi-metal synergistic effect. [ABSTRACT FROM AUTHOR]

MgH2 has a high hydrogen content of 7.6 wt% and possesses good reversibility under normal conditions. However, pristine MgH2 requires a high temperature above 300 °C to release hydrogen, with very slow kinetics. In this work, we utilized Ti3CN MXene to reduce the operating temperature and enhance the kinetics of MgH2. The initial temperature of MgH2 decomposition can be lowered from 322 °C for pristine MgH2 to 214 °C through the employment of Ti3CN. The desorbed MgH2 + 7.5 wt% Ti3CN can start absorption at room temperature, while the desorbed pristine MgH2 can only start absorption at 120 °C. The employment of Ti3CN can significantly improve the hydrogen release kinetics of MgH2, with the desorption activation energy decreasing from 121 to 80 kJ mol−1. Regarding thermodynamics, the desorption enthalpy changes of MgH2 and MgH2 + 7.5 wt% Ti3CN were 79.3 and 78.8 kJ mol−1, respectively. This indicates that the employment of Ti3CN does not alter the thermal stability of MgH2. Phase evolution studies through the use of X-ray diffraction and electron diffraction both confirm that Ti3CN remains stable during the hydrogen release and uptake process of the composite. This work will help understand the impact of a transition metal carbonitride on the hydrogen storage of MgH2. [ABSTRACT FROM AUTHOR]