Fumin Tang

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 β-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 β-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 β-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.

Synergetic enhancement of plasmonic hot-electron injection in Au cluster-nanoparticle/C3N4 for photocatalytic hydrogen evolution

Photocatalytic hydrogen evolution driven by abundant sunlight is critical for the effective conversion of renewable energy. Here, we present a combination of Au clusters and nanoparticles (NPs) on a graphitic carbon nitride (g-C3N4) semiconductor to achieve efficient plasmonic hot electron injection for realizing high visible and near-infrared photocatalytic hydrogen evolution activity. Ultraviolet photoelectron and transient photovoltage spectroscopy demonstrate that the synergetic electron coupling between Au clusters and NPs via strong sp2 hybridization with the C3N4 host could effectively tune the semiconductor work function for reducing the metal/semiconductor interfacial Schottky barrier by 0.6 eV, which greatly shortens the injection time and prolongs the average lifetime of energetic hot electrons in C3N4 by one order of magnitude under visible and near-infrared irradiation. Hence, the as-obtained Au cluster-NP/C3N4 photocatalyst achieves a prominent photocatalytic H2 production rate of 230 μmol g−1 h−1 in the light absorption range of 400–900 nm, which is 6–20 times those of its Au NP/C3N4 and Au cluster/C3N4 counterparts.

Strongly electrophilic heteroatoms confined in atomic CoOOH nanosheets realizing efficient electrocatalytic water oxidation

Developing active and durable oxygen evolution reaction (OER) electrocatalysts is greatly desired for worldwide renewable energy applications. Here, via an efficient electrophilic extraction of local electrons in cobalt oxyhydroxide (CoOOH) nanosheets realized by confining high-valence transition-metal ions (Mn4+) in cation sites of the basal plane, we significantly facilitate the proton–electron transfer kinetics and reduce the charge transfer resistance by more than 50% for high-efficiency water oxidation. The as-synthesized Mn-doped CoOOH nanosheets exhibit an excellent OER performance with a quite low overpotential of 255 mV at 10 mA cm−2 and a small Tafel slope of ∼38 mV dec−1. X-ray absorption spectroscopy and first-principles calculations demonstrate that the high-valence Mn4+ ion with an unpaired 3d3 configuration extracts local electrons from Co active sites and reduces the adsorption free energy of OH by 0.7 eV for efficient oxygen evolution.

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.

A metal-vacancy-solid-solution NiAlP nanowall array bifunctional electrocatalyst for exceptional all-pH overall water splitting

The development of active and durable bifunctional electrocatalysts for overall water splitting in a wide pH range is highly desirable for industrial water electrolysis. Herein, we develop a new type of 3D metal-vacancy solid-solution NiAlP nanowall array synthesized by a combination of selective alkali-etching and phosphorization strategies as a highly-active and earth-abundant all-pH bifunctional electrocatalyst for efficient overall water splitting. These metal-vacancy NiAlδP nanowall arrays as both the anode and cathode are highly efficient in overall-water-splitting catalysis, realizing 10 mA cm−2 at quite low cell voltages of 1.50–1.70 V for pH = 0–14. In particular, the NiAlδP nanowall arrays could achieve an outstanding overall water splitting activity in acidic electrolyte (pH = 0) with high turnover frequencies of ∼11 000 H2 per h and ∼5000 O2 per h at 50 and 300 mV overpotentials for the HER and OER, respectively, far exceeding those of the best noble-metal-free catalysts and the Pt/C–RuO2 combination.

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.