Impact Electrochemistry of MoS2: Electrocatalysis and Hydrogen Generation at Low Overpotentials

Sulfur-Bridged Iron and Molybdenum Catalysts for Electrocatalytic Ammonia Synthesis

Carbon zero electrocatalytic nitrogen reduction reaction (NRR), converting N2 to NH3 under ambient temperature and pressure, offers a sustainable alternative to the energy-intensive Haber-Bosch process. Nevertheless, NRR still faces major challenges due to direct dissociation of the strong N≡N triple bond, poor selectivity, as well as other issues related to the inadequate adsorption, activation and protonation of N2. In nature's nitrogen fixation, microorganisms are able to convert N2 to ammonia at ambient temperature and pressure, and in aqueous environment, thanks to the nitrogenase enzymes. The core NRR performance is achieved with sulfur-rich Fe transition metal clusters as active site cofactors to capture and reduce N2, with optimum performance found for Fe-Mo clusters. Because of this reason, artificial analogs in Fe-Mo coordination chemistry have been explored. However, the studies of sulfur coordinated Fe, Mo catalysts for electrocatalytic ammonia synthesis are scarce. In this review, the recent progress of Fe-Mo sulfur-bridged catalysts (including sulfur-coordinated single-site catalysts in carbon frameworks and MoS2-based catalysts) and their activities for the ammonia synthesis from nitrate reduction reaction (NO3 -RR) and nitrogen reduction reaction (NRR) are summarized. Further existing challenges and future perspectives are also discussed.

Molecular precursors for the electrodeposition of 2D-layered metal chalcogenides

Two-dimensional transition metal dichalcogenides (TMDCs) are highly anisotropic, layered semiconductors, with the general formula ME2 (M = metal, E = sulfur, selenium or tellurium). Much current research in this field focusses on TMDCs for catalysis and energy applications; they are also attracting great interest for next-generation transistor and optoelectronic devices. The latter high-tech applications place stringent requirements on the stoichiometry, crystallinity, morphology and electronic properties of monolayer and few-layer materials. As a solution-based process, wherein the material grows specifically on the electrode surface, electrodeposition offers great promise as a readily scalable, area-selective growth process. This Review explores the state-of-the-art for TMDC electrodeposition, highlighting how the choice of precursor (or precursors), solvent and electrode designs, with novel 'device-ready' electrode geometries, influence their morphologies and properties, thus enabling the direct growth of ultrathin, highly anisotropic 2D TMDCs and much scope for future advances.

Comparative Studies of Atomically Thin Proton Conductive Films to Reduce Crossover in Hydrogen Fuel Cells

Hydrogen fuel cells based on proton exchange membrane fuel cell (PEMFC) technology are promising as a source of clean energy to power a decarbonized future. However, PEMFCs are limited by a number of major inefficiencies; one of the most significant is hydrogen crossover. In this work, we comprehensively study the effects of two-dimensional (2D) materials applied to the anode side of the membrane as H2 barrier coatings on Nafion to reduce crossover effects on hydrogen fuel cells, while studying adverse effects on conductivity and catalyst performance in the beginning of life testing. The barrier layers studied include graphene, hexagonal boron nitride (hBN), amorphous boron nitride (aBN), and varying thicknesses of molybdenum disulfide (MoS2), all chosen due to their expected stability in a fuel cell environment. Crossover mitigation in the materials studied ranges from 4.4% (1 nm MoS2) to 46.1% (graphene) as compared to Nafion 211. Effects on proton conductivity are also studied, suggesting high areal proton transport in materials previously thought to be effectively nonconductive, such as 2 nm MoS2 and amorphous boron nitride under the conditions studied. The results indicate that a number of 2D materials are able to improve crossover effects, with those coated with 8 nm MoS2 and 1 L graphene able to achieve greater crossover reduction while minimizing conductivity penalty.