Encapsulating N‑doped graphite carbon in MoO2 as a novel cocatalyst for boosting photocatalytic hydrogen evolution

Bifunctional CdS-MoO2 catalysts for selective oxidation of lactic acid coupled with photocatalytic H2 production

The persistent hurdles of charge rapid recombination, inefficient use of light and utilization of sacrificial reagents have plagued the field of photocatalytic hydrogen evolution (PHE). In this research, tiny MoO2 nanoparticles of 10 nm in diameter were prepared through a straightforward solvothermal approach with a specific ratio of oleylamine and oleic acid as stabilizers. The critical factor in the synthesis process was found to be the ratio of oleylamine to oleic acid. Moreover, a two-phase interface assembly method facilitated the uniform deposition of MoO2 onto CdS nanorods. Due to the localized plasmonic-thermoelectric effect on the surface of MoO2 along with its abundant oxygen vacancies, the composite catalyst exhibited outstanding photo-utilization efficiency and an abundance of active sites. The CdS-MoO2 composite displayed a unique photochemical property in transforming lactic acid into pyruvic acid and generating hydrogen simultaneously. After exposure to artificial sunlight for 4 h, significant values of 4.7 and 3.7 mmol⋅g-1⋅h-1 were achieved for hydrogen production and pyruvic acid formation, respectively, exceeding CdS alone by 3.29 and 4.02-fold, while the selectivity of pyruvic acid was 95.68 %. Furthermore, the S-Scheme electron transport mechanism in the composites was elucidated using Electron Paramagnetic Resonance (EPR) spectroscopy, radical trapping experiments, energy band structure analysis, and the identification of critical intermediates in the process of selective oxidation. This work sheds light on the design and preparation of high-performance photocatalysts for biorefining coupled with efficient hydrogen evolution.

Current Progress of Mo-Based Metal Organic Frameworks Derived Electrocatalysts for Hydrogen Evolution Reaction

As an important half-reaction for electrochemical water splitting, electrocatalytic hydrogen evolution reaction suffers from sluggish kinetics, and it is still urgent to search high efficiency non-platinum-based electrocatalysts. Mo-based catalysts such as Mo2 C, MoO2 , MoP, MoS2 , and MoNx have emerged as promising alternatives to Pt/C owing to their similar electronic structure with Pt and abundant reserve of Mo. On the other hand, due to the adjustable topology, porosity, and nanostructure of metal organic frameworks (MOFs), MOFs are extensively used as precursors to prepare nano-electrocatalysts. In this review, for the first time, the progress of Mo-MOFs-derived electrocatalysts for hydrogen evolution reaction is summarized. The preparation method, structures, and catalytic performance of the catalysts are illustrated based on the types of the derived electrocatalysts including Mo2 C, MoO2 , MoP, MoS2 , and MoNx . Especially, the commonly used strategies to improve catalytic performance such as heteroatoms doping, constructing heterogeneous structure, and composited with noble metal are discussed. Moreover, the opportunities and challenges in this area are proposed to guide the designment and development of Mo-based MOF derived electrocatalysts.

Constructing CoAl-LDO/MoO3-x S-scheme heterojunctions for enhanced photocatalytic CO2 reduction

Converting CO2 into chemicals and fuels by solar energy can alleviate global warming and solve the energy crisis. In this work, CoAl-LDO/MoO3-x (LDO/MO) composites were successfully prepared and achieved efficient CO2 reduction under visible light. The CoAl-layered double oxides (CoAl-LDO) evolved from CoAl-layered double hydroxide (CoAl-LDH) exhibited a more robust structure, broader light absorption, and improved CO2 adsorption ability. The local surface plasmon resonance (LSPR) effect excited by nonstoichiometric MoO3-x broadened the photo-response range of CoAl-LDO/MoO3-x. In addition, constructing step-scheme (S-scheme) heterojunctions could simultaneously optimize the migration mechanism of photogenerated electrons and holes, and retain carriers with strong redox ability. Therefore, the production rates of CO and CH4 on the optimal LDO/MO composite were 7 and 9 times higher than the pristine CoAl-LDH, respectively. This work hybridizes oxidation photocatalysts and LDO-based materials to optimize the charge separation and migration mechanisms, which guides the modification of LDO-based materials.

Soft-template derived Ni/Mo2C hetero-sheet arrays for large current density hydrogen evolution reaction

Practical structural design and electronic regulation are significant for synthesising efficient electrocatalysts. Therefore, a facile soft-template approach has been applied to successfully grow Ni/Mo₂C heterojunction nanosheet arrays on nickel foam (NF) skeleton (NS-Ni/Mo₂C@NF) using polyvinylpyrrolidone (PVP) as a soft template. The density functional theory (DFT) calculations reveal that abundant Ni/Mo₂C heterojunction in NS-Ni/Mo₂C@NF can provide many active sites with a moderate hydrogen adsorption free energy (ΔG_H*, 0.037 eV). Benefiting from this nanosheet array structure and abundant Ni/Mo₂C heterojunctions, the NS-Ni/Mo₂C@NF catalyst can efficiently catalyze HER, especially at large current densities. As a result, only 151 and 271 mV overpotentials are needed to deliver 100 and 1000 mA/cm² HER, respectively. More importantly, the hydrogen production testing with NS-Ni/Mo₂C@NF as the working electrode can run stably for 500 h without activity decay under the current density of 500 mA/cm² commonly used in industrial water electrolyzers, indicating that NS-Ni/Mo₂C@NF has broad application prospects.

Synthesis of bifunctional NiFe layered double hydroxides (LDH)/Mo-doped g-C3N4 electrocatalyst for efficient methanol oxidation and seawater splitting

To boost the oxygen evolution reaction (OER) and methanol oxidation reaction (MOR) of pristine NiFe-layered double hydroxides (LDH), the NiFe-LDH/Mo-doped graphitic carbon nitride (NiFe-LDH/MoCN) heterojunction was synthesized herein through hydrothermal method. The establishment of built-in electric field in NiFe-LDH/MoCN heterojunction enhanced the electrochemical oxidation activities towards both seawater splitting and methanol oxidation, via the improving electrocatalyst surface wettability and conductivity. Almost 10-fold enhancement of turnover frequency (TOF) and electrochemical active surface area (ECSA) than pure NiFe-LDH implied more active sites to participate in catalytic reactions via Mo doping and the formation of heterostructure. Moreover, the local charge redistribution demonstrated in the NiFe-LDH/MoCN interface region may favor the adsorption of methanol and OH^- in the seawater. The present work may expound the strong coupling interaction and the establishment of built-in electric field in the interface between NiFe-LDH and semiconductor to enhance both methanol oxidation and seawater oxidation for NiFe-LDH.