We have analyzed the unusual electronic structure of Sr2FeMoO6 combining ab initio and model Hamiltonian approaches. Our results indicate that there are strong enhancements of the intra-atomic exchange strength at the Mo site as well as the antiferromagnetic coupling strength between Fe and Mo sites. We discuss the possibility of a negative effective Coulomb correlation strength ( U(eff)) at the Mo site due to these renormalized interaction strengths.

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Electrocatalytic water-splitting, a combination of oxygen and hydrogen evolution reactions (OER and HER), is highly attractive in clean energy technologies, especially for high-purity hydrogen production, whereas developing stable, earth-abundant, bifunctional catalysts has continued to pose major challenges. Herein, a mesoporous NiFe-oxide nanocube (NiFe-NC) system is developed from a NiFe Prussian blue analog metal-organic framework as an efficient bifunctional catalyst for overall water-splitting. The NiFe-NCs with ∼200 nm side length have a Ni/Fe molar ratio of 3:2 and is a composite of NiO and α/γ-FeO. The NCs demonstrate overpotentials of 271 and 197 mV for OER and HER, respectively, in 1 M KOH at 10 mA cm, which outperform those of 339 and 347 mV for the spherical NiFe-oxide nanoparticles having a similar composition. The electrolyzer constructed using NiFe-NCs requires an impressive cell voltage of 1.67 V to deliver a current density of 10 mA cm. Along with a mesoporous structure with a broad pore size distribution, the NiFe-NCs demonstrate the qualities of a desired corrosion-resistant water-splitting catalyst with long-term stability. The exposure of active sites at the edges and vertices of the NCs was validated to play a crucial role in their overall catalytic performance.

Exploring earth-abundant electrocatalysts with Pt-like performance toward alkaline hydrogen evolution reaction (HER) is extremely desirable for the hydrogen economy but remains challenging. Herein, density functional theory (DFT) predictions reveal that the electronic structure and localized charge density at the heterointerface of NiP2–FeP2 can be significantly modulated upon coupling with metallic Cu, resulting in optimized proton adsorption energy and reduced barrier for water dissociation, synergistically boosting alkaline HER. Motivated by theoretical predictions, we developed a facile strategy to fabricate interface-rich NiP2–FeP2 coupled with Cu nanowires (CuNW) grown on Cu foam (NiP2–FeP2/CuNW/Cuf). Benefiting from the superior intrinsic activity, conductivity, and copious active sites, the obtained catalyst exhibited exceptional alkaline HER activity requiring a low overpotential of 23.6 mV at −10 mA/cm2, surpassing the state-of-the-art Pt. Additionally, a full electrolyzer required a cell voltage of 1.42/1.4 V at 10 mA/cm2 in alkaline water/seawater with promising stability. This work highlights a design principle for advanced HER catalysts and beyond.