Potential-driven surface active structure rearrangement over FeP@NC towards efficient electrocatalytic hydrogen evolution.

Understanding the variation of active structure during the hydrogen evolution reaction (HER) process is of great importance for aiding in the design of optimized electrocatalysts. Herein, we present a composite material of FeP nanoparticles coated by N-doped carbon (FeP@NC) as an efficient HER electrocatalyst, synthesized by a pyrolysis and equivalent-volume impregnation method. The as-prepared FeP@NC catalyst can accelerate the HER at a small overpotential of 135 mV with a current density of 10 mA cm-2 in acidic medium and also shows a robust long-term stability with a minor decay of about 10% of the initial current density after 15 h. Using in situ X-ray absorption spectroscopy (XAS), a potential-dependent surface rearrangement of a surface pentahedral Fe structure into an octahedral Fe moiety via surface hydroxylation is clearly observed during the HER process, resulting in a much higher electrocatalytic activity. The theoretical calculations further unveil that the rearrangement of the surface FeP5(OH) octahedral structure could effectively trigger the adjacent P atoms to act as favorable proton acceptor sites towards improving the reaction kinetics of the Volmer step for efficient electrochemical hydrogen evolution.

Fast Photoelectron Transfer in (Cring)-C3N4 Plane Heterostructural Nanosheets for Overall Water Splitting.

Direct and efficient photocatalytic water splitting is critical for sustainable conversion and storage of renewable solar energy. Here, we propose a conceptual design of two-dimensional C3N4-based in-plane heterostructure to achieve fast spatial transfer of photoexcited electrons for realizing highly efficient and spontaneous overall water splitting. This unique plane heterostructural carbon ring (Cring)-C3N4 nanosheet can synchronously expedite electron-hole pair separation and promote photoelectron transport through the local in-plane π-conjugated electric field, synergistically elongating the photocarrier diffusion length and lifetime by 10 times relative to those achieved with pristine g-C3N4. As a result, the in-plane (Cring)-C3N4 heterostructure could efficiently split pure water under light irradiation with prominent H2 production rate up to 371 µmol g-1 h-1 and a notable quantum yield of 5% at 420 nm.

Oxyhydroxide Nanosheets with Highly Efficient Electron-Hole Pair Separation for Hydrogen Evolution.

The facile electron-hole pair recombination in earth-abundant transition-metal oxides is a major limitation for the development of highly efficient hydrogen evolution photocatalysts. In this work, the thickness of a layered ß-CoOOH semiconductor that contains metal/hydroxy groups was reduced to obtain an atomically thin, two-dimensional nanostructure. Analysis by ultrafast transient absorption spectroscopy revealed that electron-hole recombination is almost suppressed in the as-prepared 1.3 nm thick ß-CoOOH nanosheet, which leads to prominent electron-hole separation efficiencies of 60-90 % upon irradiation at 350-450 nm, which are ten times higher than those of the bulk counterpart. X-ray absorption spectroscopy and first-principles calculations demonstrate that [HO-CoO6-x] species on the nanosheet surface promote H(+) adsorption and H2 desorption. An aqueous suspension of the ß-CoOOH nanosheets exhibited a high hydrogen production rate of 160 µmol g(-1) h(-1) even when the system was operated for hundreds of hours.

Operando Insight into the Oxygen Evolution Kinetics on the Metal-Free Carbon-Based Electrocatalyst in an Acidic Solution.

Operando insight into the catalytic kinetics under working conditions is important for further rationalizing the design of advanced catalysts toward efficient renewable energy applications. Here, we enable a ubiquitous carbon material as an efficient acidic oxygen evolution reaction (OER) electrocatalyst, synthesized via a facile and controllable "amino-assisted polymerization and carbonization" strategy. This as-developed metal-free amino-rich hierarchical-network carbon (amino-HNC) framework directly supported on carbon paper can catalyze OER at a quite low overpotential of 281 mV and a small Tafel slope of 96 mV dec-1 in an acid solution, and maintain ∼98% of its initial catalytic activity after 100 h oxygen evolution operation. By using the operando synchrotron infrared spectroscopy, a crucial structurally evolved H2N-(*O-C)-C, formed by adsorbing the *O intermediate on the active H2N-C═C moiety, is observed on amino-HNC electrocatalysts during the OER process in the acid medium. Furthermore, theoretical calculations reveal that the optimization of the sp2 electronic structure of C═C by amino radicals could effectively lower the kinetic formation barrier of the *O intermediate on the H2N-C═C moiety, contributing to a prominent acidic oxygen-involved catalysis.

Smoothing Surface Trapping States in 3D Coral-Like CoOOH-Wrapped-BiVO4 for Efficient Photoelectrochemical Water Oxidation.

Highly efficient oxygen evolution driven by abundant sunlight is a key to realize overall water splitting for large-scale conversion of renewable energy. Here, we report a strategy for the interfacial atomic and electronic coupling of layered CoOOH and BiVO4 to deactivate the surface trapping states and suppress the charge-carrier recombination for high photoelectrochemical (PEC) water oxidation activity. The successful synthesis of a 3D ultrathin-CoOOH-overlayer-coated coral-like BiVO4 photoanode effectively tailors the migration route of photocarriers on the semiconductor/liquid interface to realize a great increase of ∼200% in the photovoltage relative to bare BiVO4, consequently decreasing the corresponding onset potential of PEC water splitting from 0.60 to 0.20 VRHE. As a result, the unique CoOOH/BiVO4 photoanode could efficiently perform PEC water oxidation in a neutral aqueous solution (pH = 7) with a high photocurrent density of 4.0 mA/cm2 at 1.23 VRHE and a prominent quantum efficiency of 65% at 450 nm. Electronic structural characterizations and theoretical calculations reveal that the combination of layered CoOOH and BiVO4 forming interfacial oxo-bridge bonding could greatly eliminate surface trapping states and promote the direct transfer of photogenerated holes from the valence band to the surface water redox potential for water oxidation.

Strong Surface Hydrophilicity in Co-Based Electrocatalysts for Water Oxidation.

Developing efficient and durable oxygen evolution electrocatalyst is of paramount importance for the large-scale supply of renewable energy sources. Herein, we report the design of significant surface hydrophilicity based on cobalt oxyhydroxide (CoOOH) nanosheets to greatly improve the surface hydroxyl species adsorption and reaction kinetics at the Helmholtz double layer for high-efficiency water oxidation activity. The as-designed CoOOH-graphene nanosheets achieve a small surface water contact angle of ∼23° and a large double-layer capacitance (Cdl) of 8.44 mF/cm2 and thus could evidently strengthen surface species adsorption and trigger electrochemical oxygen evolution reaction (OER) under a quite low onset potential of 200 mV with an excellent Tafel slope of 32 mV/dec. X-ray absorption spectroscopy and first-principles calculations demonstrate that the strong interface electron coupling between CoOOH and graphene extracts partial electrons from the active sties and increases the electron state density around the Fermi level and effectively promotes the surface intermediates formation for efficient OER.