Complete Water Splitting on MoSiGeN₄ Monolayer in Neutral Electrolytes Based on the OH*-Reservoir Mechanism

Most water splitting studies have been investigated in acidic or alkaline electrolytes, while achieving efficient water splitting in safer and lower-cost neutral electrolytes remains challenging. The oxygen evolution reaction (OER) mechanism in neutral electrolytes is still nearly blank and elusive. We investigate the complete water splitting in neutral electrolytes on the semiconductor MoSiGeN₄ monolayer. For OER, Gibbs free energy calculations revealed the highest catalytic activity (η = 0.64 V) at a biaxial strain of 4%. For the hydrogen evolution reaction (HER), ΔG_H* is calculated in the existence of pre-adsorbed OH*, the Ge-N layer has the highest catalytic activity (ΔG_H* = -0.03 eV) at biaxial strain of 2%. The OH*-reservoir mechanism for OER and HER is summarized for the first time, since OH* is stored on the Ge sites when OH* is not required for HER, and OH* is released when OH* is required to be involved in each step of intermediates (OH*, O*, and OOH*) formation for OER. The involvement of OH* effectively reduces the energy barrier for the intermediates formation of neutral water splitting, resulting in an optimal reaction pathway. This work provides a promising strategy to promote the splitting of abundant neutral water, which can be utilized in the field of clean and sustainable energy.