Subsurface Engineering Induced Fermi Level De-pinning in Metal Oxide Semiconductors for Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting is a promising approach for renewable solar light conversion. However, surface Fermi level pinning (FLP), caused by surface trap states, severely restricts the PEC activities. Theoretical calculations indicate subsurface oxygen vacancy (sub-O-v) could release the FLP and retain the active structure. A series of metal oxide semiconductors with sub-O-v were prepared through precisely regulated spin-coating and calcination. Etching X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and electron energy loss spectra (EELS) demonstrated O-v located at sub similar to 2-5 nm region. Mott-Schottky and open circuit photovoltage results confirmed the surface trap states elimination and Fermi level de-pinning. Thus, superior PEC performances of 5.1, 3.4, and 2.1 mA cm(-2) at 1.23 V vs. RHE were achieved on BiVO4, Bi2O3, TiO2 with outstanding stability for 72 h, outperforming most reported works under the identical conditions

Rationally designed ultrathin Ni(OH)2/titanate nanosheet heterostructure for photocatalytic CO2 reduction

Dye-sensitized photocatalysis has been extensively studied for photocatalytic solar energy conversion due to the advantage in capturing long-wavelength photons with a high absorption coefficient. The rational integration of photosensitizer with semiconductor and cocatalyst to collaboratively operate in one system is highly desired. Here, we fabricate a Ni(OH)2-loaded titanate nanosheet (Ni(OH)2/H2Ti6O13) composite for high-performance dye-sensitized photocatalytic CO2 reduction. The ultrathin H2Ti6O13 nanosheets with negative surface charge provide an excellent support to anchor the dye photosensitizer, while the loaded Ni(OH)2 serves as an adsorbent of CO2 and electron sink of photoelectrons. As such, the photoelectrons derived from the [Ru(bpy)3]Cl2 sensitizer can be targeted transfer to the Ni(OH)2 active sites via the H2Ti6O13 nanosheets linker. A high CO production rate of 1801 μmol g-1 h-1 is obtained over the optimal Ni(OH)2/H2Ti6O13, while the pure H2Ti6O13 shows significantly lower CO2 reduction performance. The work is anticipated to trigger more research attention on the rational design and synthesis of earth-abundant transition metal-based cocatalysts decorated on ultrathin 2D platforms for artificially photocatalytic CO2 reduction

Interfacial Engineering Promoting Electrosynthesis of Ammonia over Mo/Phosphotungstic Acid with High Performance

Electrochemical nitrogen reduction reaction (eNRR) is recognized as a promising approach for ammonia synthesis, which is, however, impeded by the inert nitrogen and the unavoidable competing hydrogen evolution reaction (HER). Here, a Mo-PTA@CNT electrocatalyst in which Mo species are anchored on the fourfold hollow sites of phosphotungstic acid (PTA) and closely embedded in multi-walled carbon nanotubes (CNT) for immobilization is designed and synthesized. Interestingly, the catalyst presents a high ammonia yield rate of 51 +/- 1 mu g h(-1) mg(cat.)(-1) and an excellent Faradaic efficiency of 83 +/- 1% at -0.1 V versus RHE under ambient conditions. The concentrations of NH4+ are also quantitatively calculated by H-1 NMR spectra and ion chromatography. Isotopic labeling identifies that the N atom of the formed NH3 originates from N-2. The controlled experiments confirm a strong interaction between Mo-PTA and N-2 with an adsorption energy of 50.46 kJ mol(-1) and activation energy of 21.36 kJ mol(-1). More importantly, due to CNT's gas storage and hydrophobicity properties, there is a fourfold increase in N-2 content. The concentration of H2O is reduced by more than half at the interface of the electrode. Thus, the activity of eNRR can be significantly improved with ultrahigh electron selectivity

Asymmetric Coordination Induces Electron Localization at Ca Sites for Robust CO2 Electroreduction to CO

Main group single atom catalysts (SACs) are promising for CO2 electroreduction to CO by virtue of their ability in preventing the hydrogen evolution reaction and CO poisoning. Unfortunately, their delocalized orbitals reduce the CO2 activation to *COOH. Herein, an O doping strategy to localize electrons on p-orbitals through asymmetric coordination of Ca SAC sites (Ca-N3O) is developed, thus enhancing the CO2 activation. Theoretical calculations indicate that asymmetric coordination of Ca-N3O improves electron-localization around Ca sites and thus promotes *COOH formation. X-ray absorption fine spectroscopy shows the obtained Ca-N3O features: one O and three N coordinated atoms with one Ca as a reactive site. In situ attenuated total reflection infrared spectroscopy proves that Ca-N3O promotes *COOH formation. As a result, the Ca-N3O catalyst exhibits a state-of-the-art turnover frequency of ≈15 000 per hour in an H-cell and a large current density of −400 mA cm−2 with a CO Faradaic efficiency (FE) ≥ 90% in a flow cell. Moreover, Ca-N3O sites retain a FE above 90% even with a 30% diluted CO2 concentration