Ni-Based Janus Pentagonal Monolayers as Promising Water-Splitting Photocatalysts

Photocatalysts which can efficiently promote water splitting to generate hydrogen without using sacrificial reagents and cocatalysts are highly desirable. In this study, on the basis of first-principles calculations, we predict that a series of Ni-based Janus monolayers with a pentagonal structure are promising photocatalysts, where the hydrogen evolution reaction can solely be driven by photon-excited electrons. The stability of the investigated monolayers is affirmed through energetic analysis, phonon band structure calculations, and ab initio molecular dynamics simulations. From the perspective of the photocatalytic process, their high absorption coefficients (∼105 cm–1) guarantee strong light absorption, their intrinsic electric fields generated by the Janus structure are beneficial to charge transfer, and their high catalytic activity speeds up the hydrogen evolution reaction. Moreover, strain engineering turns out to be effective for tuning band alignment and improving the catalytic performance. This study provides a new type of photocatalyst with high solar-to-hydrogen efficiency

Increasing the Efficiency of Photocatalytic Water Splitting via Introducing Intermediate Bands

Photocatalytic water splitting is a potential way to utilize solar energy. To be practically useful, it is important to have a high solar-to-hydrogen (STH) efficiency. In this study, we propose a conceptually new photocatalytic water splitting model based on intermediate bands (IBs). In this new model, introducing IBs within the band gap can significantly increase the STH efficiency limit (from 30.7% to 48.1% without an overpotential and from 13.4% to 36.2% with overpotentials) compared to that in conventional single-band gap photocatalytic water splitting. First-principles calculations indicate that N-doped TiO2, Bi-doped TiO2, and P-doped ZnO have suitable IBs that can be used to construct IB photocatalytic water splitting systems. The STH efficiency limits of these three doped systems are 10.0%, 12.0%, and 19.0%, respectively, while those of pristine TiO2 and ZnO without IB are only 0.9% and 1.6%, respectively. The IB photocatalytic water splitting model proposed in this study opens a new avenue for photocatalytic water splitting design