In the photoelectrochemical (PEC) water splitting (WS) reactions, a photon is absorbed by a semiconductor, generating electron-hole pairs which are transferred across the semiconductor/electrolyte interface to reduce or oxidize water into oxygen or hydrogen. Catalytic junctions are commonly combined with semiconductor absorbers, providing electrochemically active sites for charge transfer across the interface and increasing the surface band bending to improve the PEC performance. In this review, we focus on transition metal (di)chalcogenide [TM(D)C] catalysts in conjunction with silicon photoelectrode as Earth-abundant materials systems. Surprisingly, there is a limited number of reports in Si/TM(D)C for PEC WS in the literature. We provide almost a complete survey on both layered TMDC and non-layered transition metal dichalcogenides (TMC) co-catalysts on Si photoelectrodes, mainly photocathodes. The mechanisms of the photovoltaic power conversion of silicon devices are summarized with emphasis on the exact role of catalysts. Diverse approaches to the improved PEC performance and the proposed synergetic functions of catalysts on the underlying Si are reviewed. Atomic layer deposition of TM(D)C materials as a new methodology for directly growing them and its implication for low-temperature growth on defect chemistry are featured. The multi-phase TM(D)C overlayers on Si and the operation principles are highlighted. Finally, challenges and directions regarding future research for achieving the theoretical PEC performance of Si-based photoelectrodes are provided.

Cadmium sulfide (CdS) is a semiconducting absorber for photoelectrochemical (PEC) hydrogen production with suitable electronic band structures. However, it suffers from severe photocorrosion and rapid charge recombination during the desired PEC reactions. Herein, we describe the identification of the optimal junction thickness of CdS/MoS 2 core/sheath heterojunction nanostructures by employing atomic layer deposition (ALD) techniques. ALD-grown MoS 2 sheath layers with different thicknesses were realized on single-crystalline CdS nanorod (NR) arrays on transparent conducting oxide substrates. We further monitored the resulting solar H 2 evolution performance with our heterojunction photoanodes. The results showed that the junction thickness of MoS 2 plays a key role in the reduction of photocorrosion and the enhanced photocurrent density by optimizing the charge separation. A better saturation photocurrent (∼46%) was obtained with the 7 nm-thick MoS 2 @CdS NRs than that with the bare CdS NRs. Moreover, the external quantum efficiency was increased twofold over that of the pristine CdS NRs. The ALD-grown MoS 2 @CdS heterojunction structures provides an efficient and versatile platform for hydrogen production when combining ALD-grown MoS 2 with ideal semiconducting absorbers.

Venous malformation (VM) is the most common congenital vascular malformation (CVM), which usually presents as a single lesion in the majority of cases. It also presents as a mixed lesion combined with other CVMs (e.g. lymphatic malformation and arteriovenous malformation [AVM]). Therefore, the diagnosis of VM should include an appropriate work-up, to not only confirm and characterize the VM as either extratruncular or truncular but also to diagnose or exclude the presence of other CVMs. The diagnosis of VM can be made safely using non-invasive to minimally invasive studies, which can also distinguish VM from infantile haemangioma. Invasive studies, such as venography and arteriography, are generally reserved for therapeutic planning and diagnosis of more virulent CVMs (e.g. AVM). The work-up of VM should include a complete assessment of the extent and severity of the primary VM lesion. In addition, its embryologic origin, as well as its haemodynamic characteristics and secondary effects should also be determined.

We describe the direct formation of mixed-phase (1T and 2H) MoS2 layers on Si as a photocathode via atomic layer deposition (ALD) for application in the photoelectrochemical (PEC) reduction of water to hydrogen. Without typical series-metal interfaces between Si and MoS2, our p-Si/SiOx/MoS2 photocathode showed efficient and stable operation in hydrogen evolution reactions (HERs). The resulting performance could be explained by spatially genuine device architectures in three dimensions (i.e., laterally homo and vertically heterojunction structures). The ALD-grown MoS2 overlayer with the mixed-phase 1T and 2H homojunction passivates light absorber and surface states and functions as a monolithic structure for effective charge transport within MoS2. It is also beneficial in the operation of p-i-n heterojunctions with inhomogeneous barrier heights due to the presence of mixed-phase cocatalysts. The effective barrier heights reached up to 0.8 eV with optimized MoS2 thicknesses, leading to a 670 mV photovoltage enhancement without employing buried Si p-n junctions. The fast-transient behaviors via light illumination show that the mixed-phase layered chalcogenides can serve as efficient cocatalysts by depinning the Fermi levels at the interfaces. A long-term operation of ~70 h was also demonstrated in a 0.5 M H2SO4 solution.