Internal electric field modulation by copper vacancy concentration of cuprous sulfide nanosheets for enhanced selective CO_(2) photoreduction

Although the internal electric field(IEF)of photocatalysts is acknowledged as a potent driving force for photocharge separation,modulating the IEF intensity to achieve enhanced photocatalytic performances remains a challenge.Herein,cuprous sulfide nanosheets with different Cu vacancy concentration were employed to study IEF modulation and corresponding direct charge transfer.Among the samples,Cu_(1.8)S nanosheets possessed intensified IEF intensity compared with those of Cu_(2)S and Cu_(1.95)S nanosheets,suggesting that an enhanced IEF intensity could be achieved by introducing more Cu vacancies.This intensified IEF of Cu_(1.8)S nanosheets induced numerous photogenerated electrons to migrate to its surface,and the dissociative electrons were then captured by Cu vacancies,resulting in efficient charge separation spatially.In addition,the Cu vacancies on Cu_(1.8)S nanosheets accumulated electrons as active sites to lower the energy barrier of rate-determining step of CO_(2)photoreduction,leading to the selective conversion of CO_(2)to CO.Herein,the manipulation of IEF intensity through Cu vacancy concentration regulation of cuprous sulfide photocatalysts for efficient charge separation has been discussed,providing a scientific strategy to rationally improve photocata lytic performances for solar energy conversion.

Copper/cuprous sulfide electrode: preparation and performance

Cuprous sulfide （Cu2S） is a direct band-gap p-type semiconductor with excellent ionic/electronic hybrid conductivity. Alt- hough Cu/Cu2S/sulfide or polysulfide system is adopted as counter electrode of quantum-dots-sensitized solar cells （QDSSC）, the electrode process is seldom reported. Here, the electrochemical growth of Cu2S film on a copper （Cu） surface, the redox behaviors of sulfide and polysulfide, and the all-in-solid charge-transfer properties of Cu2S film are investigated. It is clarified that the copper electrode simultaneously undergoes an activated process, a membrane growth process, and a redox phase transformation process. The solid charge-transfer capability of CuzS is quantified with a high exchange-current density of 2.27 A/cm2, which elucidates that the Cu/CuzS electrode is a qualified material for counter electrodes of QDSSC. These results aid understanding of the physicochemical mechanism of QDSSC with a polysulfide electrolyte and Cu/Cu2S counter electrode.

Tetrafunctional Cu2S thin layers on Cu2O nanowires for efficient photoelectrochemical water splitting

Photoelectrochemical （PEC） water splitting by photocathodes based on p-type semiconductors is a promising process for direct and efficient hydrogen generation. The identification of ideal photocathode materials with a high photoconversion efficiency and long-term stability is still a significant challenge. Herein, we propose a new photocathode consisting of Cu2S-coated Cu2O nanowires （NWs） supported on a three-dimensional porous copper foam. The Cu2S thin layer is generated in situ on the surface of the Cu2O NWs and has four functions： （1） sensitizer, with a band gap of 1.2 eV, for extending the range of optical absorption into the near-infrared region; （2） electron trapper, with appropriate energy level alignment to Cu2O, for achieving effective electron transfer and trapping; （3） electrocatalyst, with excellent electrocatalytic activity for the hydrogen evolution reaction; and （4） protector, preventing direct contact between Cu2O and the electrolyte in order to significantly increase the stability. A photocathode based on the tetrafunctional Cu2S-coated Cu2O NWs exhibits significantly enhanced PEC performance and remarkably improved long-term stability under illumination. The present strategy, based on the in situ generation of multifunctional layers, opens a new avenue for the rational design of photocathodes for PEC water reduction.