Electronic structure modulation of MoO2 via Er-doping for efficient overall water/seawater splitting and Mg/seawater batteries

Electronic structure modulation is an effective strategy for electrocatalysts to boost their hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities in water splitting. Here, a rational design of rare earth element Er-doped MoO2 (Er-MoO2) with modulated electronic structure is reported, leading to boosted water splitting activity in both alkaline and seawater electrolyte. Experimental results manifest that the optimized Er-MoO2 requires overpotentials of only 94/221 mV and 173/312 mV to deliver the 10 mA cm−2 for HER/OER in alkaline and seawater electrolyte, respectively. As bifunctional electrocatalysts for overall water splitting, the Er-MoO2 requires a cell voltage of only 1.52 and 1.67 V to gain 10 mA cm−2 in alkaline and seawater electrolyte, respectively. Moreover, a Mg/seawater battery coupled with the Er-MoO2 cathode achieves a maximum power density of 8.17 mW cm−2, combining with an excellent discharging stability for at least 24 h. This work provides a facile strategy toward the design of efficient non-noble metal catalysts for overall water/seawater splitting and Mg/seawater battery.