Seeking for a suitable cocatalyst to realize highly efficient photocatalytic hydrogen (H2) production is a great challenge in the field of solar energy conversion. Herein, hollow cobalt sulfide (Co...

Hollow CoSx Polyhedrons Act as High-Efficiency Cocatalyst for Enhancing the Photocatalytic Hydrogen Generation of g-C3N4

Graphene and two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted significant interest due to their unique properties that cannot be obtained in their bulk counterparts. These atomically thin 2D materials have demonstrated strong light–matter interactions, tunable optical bandgap structures and unique structural and electrical properties, rendering possible the high conversion efficiency of solar energy with a minimal amount of active absorber material. The isolated 2D monolayer can be stacked into arbitrary van der Waals (vdWs) heterostructures without the need to consider lattice matching. Several combinations of 2D/3D and 2D/2D materials have been assembled to create vdWs heterojunctions for photovoltaic (PV) and photoelectrochemical (PEC) energy conversion. However, the complex, less-constrained, and more environmentally vulnerable interface in a vdWs heterojunction is different from that of a conventional, epitaxially grown heterojunction, engendering new challenges for surface and interface engineering. In this review, the physics of band alignment, the chemistry of surface modification and the behavior of photoexcited charge transfer at the interface during PV and PEC processes will be discussed. We will present a survey of the recent progress and challenges of 2D/3D and 2D/2D vdWs heterojunctions, with emphasis on their applicability to PV and PEC devices. Finally, we will discuss emerging issues yet to be explored for 2D materials to achieve high solar energy conversion efficiency and possible strategies to improve their performance.

Engineering graphene and TMDs based van der Waals heterostructures for photovoltaic and photoelectrochemical solar energy conversion

Graphitic carbon nitride (g-C3N4) has emerged as one of the most promising photocatalysts due to its metal-free nature, abundance of raw material, and thermal physical–chemical stability. The breakthrough research studies in recent years have mostly been concentrated on the engineering of the intrinsic and morphological properties of g-C3N4-based photocatalysts in the framework of powder suspensions for artificial photosynthesis and environmental remediation. However, practical applications of g-C3N4-based electrodes and devices are still in the early stages of development due to challenging fabrication methods of g-C3N4 thin films. This review addresses the classification of diverse techniques to deposit g-C3N4-based thin films and explores a broad spectrum of applications pertinent to g-C3N4-based electrodes. Although this paper is principally focused on photoelectrochemical water splitting, other emerging applications of g-C3N4 in solar cells, electrocatalysts and supercapacitors are also reviewed. Lastly, further suggestions are posited for other potential applications, challenges and future orientations.

Graphitic carbon nitride (g-C3N4) electrodes for energy conversion and storage: a review on photoelectrochemical water splitting, solar cells and supercapacitors

Enhanced photocatalytic H2 production over dual-cocatalyst-modified g-C3N4 heterojunctions

Hierarchical Cu2O foam/g-C3N4 photocathode for photoelectrochemical hydrogen production

A Cu2O/g-C3N4/WS2 triple-layer photocathode was fabricated by using a layer-by-layer assembly method for photoelectrochemical hydrogen evolution. Cu2O was electrodeposited on the FTO as the active layer for light harvesting. The chemically inert g-C3N4 can protect the unstable Cu2O layer and form a p-n junction with Cu2O to increase the light-to-electricity conversion efficiency. Mixed-phase WS2 nanosheets were obtained through a lithium insertion method and used as an effective hydrogen evolution catalyst for photocurrent-to-hydrogen conversion. This photocathode is effective for photoelectrochemical hydrogen evolution, and a photocurrent of −9.5 mA cm−2 at −0.55 V versus RHE (pH 6.0) can be obtained under visible light (λ≥420 nm, 100 mW cm−2).

Xintian Xu

Papers

Fabrication of a Cu2O/g‐C3N4/WS2 Triple‐Layer Photocathode for Photoelectrochemical Hydrogen Evolution