A novel crystal configuration of sandwiched S-Mo-Se structure (Janus SMoSe) at the monolayer limit has been synthesized and carefully characterized in this work. By controlled sulfurization of monolayer MoSe2 the top layer of selenium atoms are substituted by sulfur atoms while the bottom selenium layer remains intact. The peculiar structure of this new material is systematically investigated by Raman, photoluminescence and X-ray photoelectron spectroscopy and confirmed by transmission-electron microscopy and time-of-flight secondary ion mass spectrometry. Density-functional theory calculations are performed to better understand the Raman vibration modes and electronic structures of the Janus SMoSe monolayer, which are found to correlate well with corresponding experimental results. Finally, high basal plane hydrogen evolution reaction (HER) activity is discovered for the Janus monolayer and DFT calculation implies that the activity originates from the synergistic effect of the intrinsic defects and structural strain inherent in the Janus structure.

Janus Monolayer Transition Metal Dichalcogenides

The global photovoltaic (PV) market is dominated by crystalline silicon (c-Si) based technologies with heavily doped, directly metallized contacts. Recombination of photo-generated electrons and holes at the contact regions is increasingly constraining the power conversion efficiencies of these devices as other performance-limiting energy losses are overcome. To move forward, c-Si PV technologies must implement alternative contacting approaches. Passivating contacts, which incorporate thin films within the contact structure that simultaneously supress recombination and promote charge-carrier selectivity, are a promising next step for the mainstream c-Si PV industry. In this work, we review the fundamental physical processes governing contact formation in c-Si. In doing so we identify the role passivating contacts play in increasing c-Si solar cell efficiencies beyond the limitations imposed by heavy doping and direct metallization. Strategies towards the implementation of passivating contacts in industrial environments are discussed. The development of passivating contacts holds great potential for enhancing the power conversion efficiency of silicon photovoltaics. Here, De Wolf et al. review recent advances in material design and device architecture, and discuss technical challenges to industrial fabrication.

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Passivating contacts for crystalline silicon solar cells

Hydrogen production from electrochemical water splitting represents a highly promising technology for sustainable energy storage, but its widespread implementation heavily relies on the development of high-performance and cost-effective hydrogen evolution reaction (HER) electrocatalysts. Metal oxides, an important family of functional materials with diverse compositions and structures, were traditionally believed inactive towards HER. Encouragingly, the continuous breakthroughs and significant progress in recent years (mainly from 2015 onwards) make engineered metal oxides emerge as promising candidates for HER electrocatalysis. In this article, we present a comprehensive review of recent advances in metal oxide-based electrocatalysts for HER. We start with a brief description of some key fundamental concepts of HER, such as mechanisms, computational activity descriptors, and experimental parameters used to evaluate catalytic performance. This is followed by a overview of various types of metal oxide-based HER electrocatalysts reported so far, including single transition metal oxides, spinel oxides, perovskite oxides, metal (oxy)hydroxides, specially-structured metal oxides and oxide-containing hybrids, with special emphasis on designed strategies for promoting performance and property–activity correlation. Finally, some concluding remarks and perspectives about future opportunities of this exciting field are provided.

Metal oxide-based materials as an emerging family of hydrogen evolution electrocatalysts

Electrochemical water splitting is the most promising process to produce carbon-neutral hydrogen as an energy carrier, and hydrogen evolution reaction (HER) electrocatalysts are essential to reduce the energy barrier and improve hydrogen production efficiency. This driving force necessitates the design of HER electrocatalysts with low-cost, high-abundance, high activity and stability. In this review, we systemically summarize recent publications with critical insight into the advances of iron-based phosphides as HER electrocatalysts. Various synthesis strategies corresponding to different phosphating strategies for guiding iron phosphide design are described, followed by illustrations of how to boost FeP HER catalytic performance by enriching the accessible active sites and modifying the electronic structure. Finally, we point out several challenges and prospects, which can open up opportunities to design next-generation FeP HER electrocatalysts.

Iron-based phosphides as electrocatalysts for the hydrogen evolution reaction: recent advances and future prospects

Hydrogen has been deemed as an ideal substitute fuel to fossil energy because of its renewability and the highest energy density among all chemical fuels One of the most economical, ecofriendly, and high-performance ways of hydrogen production is electrochemical water splitting Recently, 2D transition metal dichalcogenides (also known as 2D TMDs) showed their utilization potentiality as cost-effective hydrogen evolution reaction (HER) catalysts in water electrolysis Herein, recent representative research efforts and systematic progress made in 2D TMDs are reviewed, and future opportunities and challenges are discussed Furthermore, general methods of synthesizing 2D TMDs materials are introduced in detail and the advantages and disadvantages for some specific methods are provided This explanation includes several important regulation strategies of creating more active sites, heteroatoms doping, phase engineering, construction of heterostructures, and synergistic modulation which are capable of optimizing the electrical conductivity, exposure to the catalytic active sites, and reaction energy barrier of the electrode material to boost the HER kinetics In the last section, the current obstacles and future chances for the development of 2D TMDs electrocatalysts are proposed to provide insight into and valuable guidelines for fabricating effective HER electrocatalysts

2D Transition Metal Dichalcogenides: Design, Modulation, and Challenges in Electrocatalysis.

Nitrogen-doped carbon-decorated yolk-shell CoP@FeCoP micro-polyhedra derived from MOF for efficient overall water splitting

Numerous efforts in improving the hydrogen evolution reaction (HER) performance of transition metal dichalcogenides mostly focus on active sites exposing, vacancy engineering, and phase engineering...

Magnetic Enhancement for Hydrogen Evolution Reaction on Ferromagnetic MoS2 Catalyst.

A MoS2 moire superlattice with a twisted angle of θ ≈ 7.3° via a facile method instead of a conventional mechanical stacking method is successfully fabricated. With reduced interlayer potential bar...

MoS2 Moiré Superlattice for Hydrogen Evolution Reaction

Monolayer MoS2 films with substantial sulfur vacancies are obtained using the laser molecular beam epitaxy (L-MBE) technique benefitted by high substrate temperature and ultrahigh vacuum growth conditions. The intrinsic sulfur vacancies present an excellent opportunity for varying the work function of monolayer MoS2 films by nitrogen doping. The in-plane doping of nitrogen atoms on L-MBE-synthesized monolayer MoS2 films is realized on the basis of rapid thermal annealing in a nitrogen environment. The as-grown and nitrogen-doped monolayer MoS2 films are evaluated by using Raman and photoluminescence spectroscopies. In accordance with the X-ray photoelectron spectroscopy results, the ultraviolet photoelectron spectroscopy investigation shows that the work function of the monolayer MoS2 films increases by 0.29 eV after covalent nitrogen doping. Nitrogen doping on monolayer MoS2 is further treated theoretically using first-principles calculations. Based on theoretical calculations and experimental validations, it is illustrated that nitrogen is a promising in-plane heteroatom dopant for work function variation of monolayer MoS2.

Manman Guo

Papers

Nitrogen-doped carbon-decorated yolk-shell CoP@FeCoP micro-polyhedra derived from MOF for efficient overall water splitting

Magnetic Enhancement for Hydrogen Evolution Reaction on Ferromagnetic MoS2 Catalyst.

MoS2 Moiré Superlattice for Hydrogen Evolution Reaction

Work function variation of monolayer MoS2 by nitrogen-doping

Porous Co3O4/CoS2 nanosheet-assembled hierarchical microspheres as superior electrocatalyst towards oxygen evolution reaction