NiFe-based electrocatalysts will experience dynamical surface reconstruction during oxygen evolution reaction (OER) process, and the derived metal (oxy)hydroxide hybrids on the surface have been considered as the actual active species for OER. Tremendous efforts have been dedicated to understanding the surface reconstruction, but there is rare research on recognizing the origin of improved performance derived from anion species of substrate. Herein, the OER electrocatalytic characteristics were tuned with different anions in NiFe-based catalyst, using NiFe-based oxides/nitride/sulfide/selenides/phosphides (NiFeX, X = O, N, S, Se, and P) as the model materials. The combination of X-ray photoelectronic spectroscopy, electrochemical tests, operando spectroscopic characterizations, and density functional theory (DFT) calculations, reveals that anion with lower electronegativity in NiFe-based catalyst leads to higher conductivity and delayed valence transition of Ni sites, as well as optimized adsorption behavior towards oxygen intermediates, contributing to enhanced OER performance. Accordingly, NiFeP electrocatalyst demonstrates an ultralow overpotential of 265 mV at 20 mA·cm⁻² for OER, as well as long-term stability. This work not only offers further insights into the effect of anionic electronegativity on the intrinsic OER electrocatalytic properties of NiFe-based electrocatalyst but also provides guide to design efficient non-noble metal-based electrocatalysts for water oxidation.

Photoelectrochemical (PEC) water splitting using semiconductors offers a promising way to convert renewable solar energy to clean hydrogen fuels. However, due to the sluggish reaction kinetics of water oxidation, significant charge recombination occurred at the photoanode/electrolyte interface and cause decrease of its PEC performance. To reduce the surface recombination, we deposit different transition metal complexes on BiVO₄ nanocone arrays by a versatile light driven in-situ two electrode photodeposition approach without applied bias. Conformal cobalt phosphate "Co-Pi" , nickel borate "Ni-Bi" and manganese phosphate "Mn-Pi" complexes were deposited on BiVO₄ nanocone arrays to form core-shell structure photoanode, all of which lead to enhanced photoelectrochemical performance. The photocurrent of the Co-Pi/BiVO₄ photoanode under front-side illumination for 5 min is increased by 4 folds comparing to that of bare BiVO₄ photoanode at 0.6 V vs. RHE, reaching a hole transfer efficiency as high as 94.5% at 1.23 V vs. RHE. The proposed photodeposition strategy is simple and efficient, and can be extended to deposite cocatalyst on other semiconductors with a valence band edge located at a potential more positive than the oxidation potential of transition metal ion in the cocatalyst.

Oxygen evolving catalyst (OEC) is a critical determinant for the efficiency of photoelectrochemical (PEC) water splitting. Here we report an approach to depositing a novel manganese borate (Mn-Bi) OER catalyst on BiVO₄ nanocone photoanode by photodeposition in sodium borate buffer solution containing Mn(Ⅱ) ions. Due to the spontaneous photo-electric-field-enhancement effect at the vertically oriented BiVO₄ nanocone structure, spherical Mn-Bi nanoparticle was selectively photodeposited at the apex of BiVO₄ nanocone. Significant improvement of photocurrent was observed for the obtained hierarchical Mn-Bi/BiVO₄ photoanode which could be ascribed to enhanced hole injection efficiency, especially in low bias region. It was observed that the injection efficiency of Mn-Bi/BiVO₄ is 98% which gave a photocurrent of 0.94 mA/cm² at 1.5 V vs. RHE.

In this study, a potentially universal new strategy is reported for the large-scale, low-cost fabrication of visible-light-active highly ordered heteronanostructures based on the spontaneous photoelectric-field-enhancement effect inherent in pyramidal morphology. The hierarchical vertically oriented arrayed structures comprise an active molecular co-catalyst at the apex of a visible-light-active large band gap semiconductor for low-cost solar water splitting in a neutral aqueous medium without the use of a sacrificial agent.