Atom-thin transition metal dichalcogenides (TMDs) have emerged as fascinating materials and key structures for electrocatalysis. So far, their edges, dopant heteroatoms and defects have been intensively explored as active sites for the hydrogen evolution reaction (HER) to split water. However, grain boundaries (GBs), a key type of defects in TMDs, have been overlooked due to their low density and large structural variations. Here, we demonstrate the synthesis of wafer-size atom-thin TMD films with an ultra-high-density of GBs, up to ~10¹² cm⁻². We propose a climb and drive 0D/2D interaction to explain the underlying growth mechanism. The electrocatalytic activity of the nanograin film is comprehensively examined by micro-electrochemical measurements, showing an excellent hydrogen-evolution performance (onset potential: −25 mV and Tafel slope: 54 mV dec⁻¹), thus indicating an intrinsically high activation of the TMD GBs.

The development of upscalable oxygen evolving electrocatalysts from earth-abundant metals able to operate in neutral or acidic environments and low overpotentials remains a fundamental challenge for the realization of artificial photosynthesis. In this study, we report a highly active phase of hetero-bimetallic cyanide-bridged electrocatalysts able to promote water oxidation under neutral, basic (pH < 13) and acidic conditions (pH > 1). Cobalt-iron Prussian blue-type thin films, formed by chemical etching of Co(OH)_1.0(CO₃)_0.5·nH₂O nanocrystals, yield a dramatic enhancement of the catalytic performance towards oxygen production, when compared with previous reports for analogous materials. Electrochemical, spectroscopic and structural studies confirm the excellent performance, stability and corrosion resistance, even when compared with state-of-the-art metal oxide catalysts under moderate overpotentials and in a remarkably large pH range. The origin of the superior electrocatalytic activity towards water oxidation appears to be in the optimized interfacial matching between catalyst and electrode surface obtained through this fabrication method.

The optimization of multiple interfaces in hematite (α-Fe₂O₃) based composites for photoelectrochemical water splitting to facilitate charge transport in the bulk is of paramount importance to obtain enhanced solar-to-fuel efficiency. Herein, we report the fabrication of ITO/Fe₂O₃/Fe₂TiO₅/FeNiOOH multi-layer nanowires and a series of systematic experiments designed to elucidate the mechanism underlying the interfacial coupling effect of the quaternary hematite composite. The hierarchical ITO/Fe₂O₃/Fe₂TiO₅/FeNiOOH nanowires display photocurrents that are more than an order of magnitude greater than those of pristine Fe₂O₃ nanowires (from 0.205 mA cm⁻² to 2.2 mA cm⁻² at 1.23 V vs. RHE and 1 Sun), and higher than those of most of the recently reported state-of-the-art hematite composites. Structural, compositional and electrochemical investigations disclose that the surface states (SS) are finely regulated via the atomic addition of an Fe₂TiO₅ layer and FeNiOOH nanodots, while the upgrading of back contact conductivity and charge donor densities originate from the epitaxial relationship and enhanced Sn doping contributed from the ITO underlayer. We attribute the superior water oxidation performance to the interfacial coupling effect of the ITO underlayer (Sn doping and back contact conductivity promoter), the atomic level Fe₂TiO₅ coating (Ti doping, surface state density and energy level modulation) and the FeNiOOH nanodot electrocatalyst (regulating surface state energy level). Our work suggests an effective pathway for rational designing of highly active and cost-effective integrated photoanodes for photoelectrochemical water splitting.

The nanostructured BiVO4 photoanodes were prepared by electrospinning and were further characterized by XRD, SEM, and XPS, confirming the bulk and surface modification of the electrodes attained by W addition. The role of surface states (SS) during water oxidation for the as-prepared photoanodes was investigated by using electrochemical, photoelectrochemical, and impedance spectroscopy measurements. An optimum 2% doping is observed in voltammetric measurements with the highest photocurrent density at 1.23 VRHE under back side illumination. It has been found that a high PEC performance requires an optimum ratio of density of surface states (NSS) with respect to the charge donor density (Nd), to give both good conductivity and enough surface reactive sites. The optimum doping (2%) shows the highest Nd and SS concentration, which leads to the high film conductivity and reactive sites. The reason for SS acting as reaction sites (i-SS) is suggested to be the reversible redox process of V5+/V4+ in semiconductor bulk to form water oxidation intermediates by electron trapping process. Otherwise, the irreversible surface reductive reaction of VO2+ to VO2+ by electron trapping process raises the surface recombination. W doping does have an effect on the surface properties of BiVO4 electrode. It can tune the electron trapping process to obtain high concentration of i-SS and less surface recombination. This work gives a further understanding for the enhancement of PEC performance caused by W doping in the field of charge transfer at the semiconductor/electrolyte interface.