Direct Synthesis of Molybdenum Phosphide Nanorods on Silicon Using Graphene at the Heterointerface for Efficient Photoelectrochemical Water Reduction

Abstract

Highlights MoP nanorod-array catalysts were directly synthesized on graphene passivated silicon photocathodes without secondary phase. Mo-O-C covalent bondings and energy band bending at heterointerfaces facilitate the electron transfer to the reaction sites. Numerous catalytic sites and drastically enhanced anti-reflectance of MoP nanorods contribute to the high solar energy conversion efficiency. Abstract Transition metal phosphides (TMPs) and transition metal dichalcogenides (TMDs) have been widely investigated as photoelectrochemical (PEC) catalysts for hydrogen evolution reaction (HER). Using high-temperature processes to get crystallized compounds with large-area uniformity, it is still challenging to directly synthesize these catalysts on silicon photocathodes due to chemical incompatibility at the heterointerface. Here, a graphene interlayer is applied between p-Si and MoP nanorods to enable fully engineered interfaces without forming a metallic secondary compound that absorbs a parasitic light and provides an inefficient electron path for hydrogen evolution. Furthermore, the graphene facilitates the photogenerated electrons to rapidly transfer by creating Mo-O-C covalent bondings and energetically favorable band bending. With a bridging role of graphene, numerous active sites and anti-reflectance of MoP nanorods lead to significantly improved PEC-HER performance with a high photocurrent density of 21.8 mA cm−2 at 0 V versus RHE and high stability. Besides, low dependence on pH and temperature is observed with MoP nanorods incorporated photocathodes, which is desirable for practical use as a part of PEC cells. These results indicate that the direct synthesis of TMPs and TMDs enabled by graphene interlayer is a new promising way to fabricate Si-based photocathodes with high-quality interfaces and superior HER performance. Graphic Abstract

Type-II Band Alignment Enhances Unassisted Photoelectrochemical Water-Splitting Performance of the BaTiO3/CdS Ferroelectric Heterostructure Photoanode under Solar Light Irradiation

“…The efficient exploitation of renewable solar energy has been regarded as a hopeful strategy to address the growing energy crisis. , Recently, considerable studies have shown that the solar light-driven photoelectrochemical (PEC) water splitting of a nanoscale semiconductor photoanode is a promising technology to use solar energy to generate hydrogen directly. , Therefore, various semiconductor photoanodes have been widely applied to split water through a PEC cell. − However, the poor absorption ability of visible light and rapid recombination of photogenerated charge carriers need to be solved for the semiconductor photoanodes to improve PEC performance. − …”

Strategies for improving photoelectrochemical water splitting performance of Si‐based electrodes

“…Because of the rareness and preciousness, noble metals are restricted in large‐scale applications. The cost‐effective and earth‐abundant candidates to catalyze HER have been developed, such as transition metal alloy (Ni‐Mo, 90 Ni‐Fe 117 ), metal phosphides (Co 2 P, 38 GaP, 46 NiCoP, 75 MoP, 76 WP, 77 ), sulfides (MoS 2 52,54,93,123 ), selenides (NiCoSe x 49 ), and CuCo hybrid oxide 116 . Most of them act as both HER catalysts and protective layers for Si‐based photocathodes.…”

Surface/Interface Engineering of Si-Based Photocathodes for Efficient Hydrogen Evolution

“…In addition to surface textures of Si, other materials with photonic nanostructures supported on planar Si surfaces can also play a role in improving light absorption. , Specifically, the TiO 2 in the form of nanorod (NR) arrays can significantly reduce the reflection of incident light on the photocathode surface and increase the ratio of specific surface area to geometric area. Thus, more active sites of the catalyst can be exposed, and the channel can be confined for short-distance photogenerated charge transport, effectively improving charge collection efficiency.…”