Photocatalytic water-splitting for hydrogen generation by sunlight provides a new route to address the energy and environmental problems. In recent years, tremendous efforts have been devoted to design highly efficient water-splitting photocatalysts. Adequate light absorption, effective photogenerated carrier separation, and sufficiently large overpotentials for water redox are crucial in achieving high solar-to-hydrogen (STH) efficiency. These parameters thus strongly influence the design of novel photocatalytic materials. Two-dimensional (2D) photocatalysts have flourished because of the large specific surface area ratio, short carrier migration distance compared to bulk photocatalysts, enormous design flexibility via van der Waals heterostrucutre (HS) engineering and many other unique capabilities that meet the criteria for high-efficiency STH conversion. In this review, we summarize the recent developments of 2D materials and HSs for water-splitting applications from a theoretical perspective. Specifically, we first discuss a number of 2D materials and HSs employed for water-splitting. We review various strategies of material designs to modulate and enhance the photocatalytic performance via improving light harvesting and carrier separation, such as the introduction of defects, dopants and the application of strain, external electric field, rotation angles, ferroelectric switching. We then discuss the methods to evaluate hydrogen evolution reaction, oxygen evolution reaction, and STH efficiency. Finally, the opportunities and challenges of designing 2D materials and HSs for water-splitting are presented.

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This paper reviews the NTIRE 2020 challenge on real image denoising with focus on the newly introduced dataset, the proposed methods and their results. The challenge is a new version of the previous NTIRE 2019 challenge on real image denoising that was based on the SIDD benchmark. This challenge is based on a newly collected validation and testing image datasets, and hence, named SIDD+. This challenge has two tracks for quantitatively evaluating image denoising performance in (1) the Bayer-pattern rawRGB and (2) the standard RGB (sRGB) color spaces. Each track ∼250 registered participants. A total of 22 teams, proposing 24 methods, competed in the final phase of the challenge. The proposed methods by the participating teams represent the current state-of-the-art performance in image denoising targeting real noisy images. The newly collected SIDD+ datasets are publicly available at: https://bit.ly/siddplus_data. A. Abdelhamed (kamel@eecs.yorku.ca, York University), M. Afifi, R. Timofte, and M.S. Brown are the NTIRE 2020 challenge organizers, while the other authors participated in the challenge. Appendix A contains the authors' teams and affiliations. NTIRE webpage: arXiv:2005.04117v1 [cs.CV] 8 May 2020

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Using hybrid density functional calculations, the influence of rotation angles on the photocatalytic performance of 2D ZnO/GaN heterostructures is explored. The results show that the bandgaps and band alignments for ZnO/GaN heterostructures can be tuned by rotation angles. Rotated ZnO/GaN heterostructures are favorable for visible light absorption. Band alignments of different rotated ZnO/GaN heterostructures are severally thermodynamically favorable for spontaneous generation of hydrogen and oxygen with the pH scope of 0–14, 3–14, 2–14, 1–14, 1–14, and 4–14. In addition, the formed built‐in electric field across ZnO/GaN heterostructure interface promotes photogenerated carrier migration and inhibits photogenerated carrier recombination. These factors make rotated ZnO/GaN heterostructures promising for visible light water splitting. The findings pay a new way to design 2D heterostructures used for photocatalytic water splitting.