Graphene-quantum-dot-modified medium-entropy (oxy)hydroxides as promising bifunctional electrocatalysts for overall water/simulated seawater splitting.

Suitable bifunctional electrocatalysts for overall water/simulated seawater splitting can veritably promote practical hydrogen applications. Here, graphene-quantum-dot-modified medium-entropy (oxy)hydroxides (FeCoNiMnOOH/GQDs) are designed with eximious electrocatalytic activity in both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). It is worth noting that FeCoNiMnOOH/GQDs obtain an impressively low overpotential of 210 mV for OER and 70 mV for HER at a current density of 10 mA cm, respectively. The two-electrode electrolyzer constructed by FeCoNiMnOOH/GQDs exhibits exceptional performance, reaching 10 mA cm with only 1.53 V (1.0 KOH) and 1.59 V (1.0 KOH + 0.5 NaCl). Additionally, the density functional theory (DFT) calculations indicate that the intense coupling of the intrinsic electronic structure brings the d-band center of metal atoms closer to the Fermi level, reducing the rate-determining step of the Gibbs free energy. Overall, the composite strategy of graphene quantum dots and medium-entropy systems offers a new approach for fabricating advanced medium/high-entropy energy conversion and storage materials.