Substitution of copper atoms into defect-rich molybdenum sulfides and their electrocatalytic activity

Modulating the Coordination Environment of Cu-Embedded MoX2 (X = S, Se, and Te) Monolayers for Electrocatalytic Reduction of CO2 to CH4: Unveiling the Origin of Catalytic Activity

The electrochemical CO2 reduction reaction (CO2RR) is a promising approach to alleviating global warming and emerging energy crises. Yet, the CO2RR efficiency is impeded by the need for electrocatalysts with good selectivity and efficiency. Recently, single-atom catalysts (SACs) have attracted much attention in electrocatalysis and are more efficient than traditional metal-based catalysts. In this study, we modeled a Cu single atom embedded on MoX2 (X = Se and Te) monolayer with a single chalcogen (X) vacancy as SAC. Employing the dispersion-corrected density functional theory (DFT-D3) method, the electrocatalytic CO2RR activity of the Cu-MoX2 SACs is systematically investigated through significant descriptors, such as the Gibbs free energy change, charge density difference, and COHP analysis. The stability of SACs, CO2 adsorption configurations, and all possible reaction pathways for the formation of C1 products (HCOOH, CO, CH3OH, and CH4) were examined. All of the Cu-MoX2 SACs are stable and show high catalytic selectivity for the CO2RR by significantly suppressing the hydrogen evolution reaction (HER). We found that the catalytic activity is mainly due to the level of antibonding states filling between the Cu atom and *OCHOH intermediate. Among the C1 products, CH4 is selectively produced in all three SACs. Notably, there is a decrease in the limiting potential (UL) when X changes from S to Te in Cu-MoX2. Among these three SACs, Cu-MoTe2 SAC is the most promising catalyst for reducing CO2 to CH4, with as low as UL of -0.34 V vs RHE. Our results demonstrate that the local coordination environment in SACs has a significant impact on the catalytic activity of CO2RR.

Rational Design of Earth-Abundant Catalysts toward Sustainability

Catalysis is crucial for clean energy, green chemistry, and environmental remediation, but traditional methods rely on expensive and scarce precious metals. This review addresses this challenge by highlighting the promise of earth-abundant catalysts and the recent advancements in their rational design. Innovative strategies such as physics-inspired descriptors, high-throughput computational techniques, and artificial intelligence (AI)-assisted design with machine learning (ML) are explored, moving beyond time-consuming trial-and-error approaches. Additionally, biomimicry, inspired by efficient enzymes in nature, offers valuable insights. This review systematically analyses these design strategies, providing a roadmap for developing high-performance catalysts from abundant elements. Clean energy applications (water splitting, fuel cells, batteries) and green chemistry (ammonia synthesis, CO2 reduction) are targeted while delving into the fundamental principles, biomimetic approaches, and current challenges in this field. The way to a more sustainable future is paved by overcoming catalyst scarcity through rational design.

Exploring the Capability of Cu-MoS2 Catalysts for Use in Electrocatalytic Overall Water Splitting

Herein, we prepare MoS2 and Cu-MoS2 catalysts using the solvothermal method, a widely accepted technique for electrocatalytic overall water-splitting applications. TEM and SEM images, standard tools in materials science, provide a clear view of the morphology of Cu-MoS2. HRTEM analysis, a high-resolution imaging technique, confirms the lattice spacing, lattice plane, and crystal structure of Cu-MoS2. HAADF and corresponding color mapping and advanced imaging techniques reveal the existence of the Cu-doping, Mo, and S elements in Cu-MoS2. Notably, Cu plays a crucial role in improving the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) of the Cu-MoS2 catalyst as compared with the MoS2 catalyst. In addition, the Cu-MoS2 catalyst demonstrates significantly lower overpotential (167.7 mV and 290 mV) and Tafel slopes (121.5 mV dec-1 and 101.5 mV dec-1), standing at -10 mA cm-2 and 10 mA cm-2 for HER and OER, respectively, compared to the MoS2 catalyst. Additionally, the Cu-MoS2 catalyst displays outstanding stability for 12 h at -10 mA cm-2 of HER and 12 h at 10 mA cm-2 of OER using chronopotentiaometry. Interestingly, the Cu-MoS2‖Cu-MoS2 cell displays a lower cell potential of 1.69 V compared with the MoS2‖MoS2 cell of 1.81 V during overall water splitting. Moreover, the Cu-MoS2‖Cu-MoS2 cell shows excellent stability when using chronopotentiaometry for 18 h at 10 mA cm-2.

Doped 2D SnS materials derived from liquid metal-solution for tunable optoelectronic devices

Gas-liquid reaction phenomena on liquid-metal solvents can be used to form intriguing 2D materials with large lateral dimensions, where the free energies of formation determine the final product. A vast selection of elements can be incorporated into the liquid metal-based nanostructures, offering a versatile platform for fabricating novel optoelectronic devices. While conventional doping techniques of semiconductors present several challenges for 2D materials. Liquid metals provide a facile route for obtaining doped 2D semiconductors. In this work, we successfully demonstrate that the doping of 2D SnS can be realized in a glove box containing a diluted H₂S gas. Low melting point elements such as Bi and In are alloyed with base liquid Sn in varying concentrations, resulting in the doping of 2D SnS layers incorporating Bi and In sulphides. Optoelectronic properties for photodetectors and piezoelectronics can be fine-tuned through the controlled introduction of selective migration doping. The structural modification of 2D SnS results in a 22.6% enhancement of the d₁₁ piezoelectric coefficient. In addition, photodetector response times have increased by several orders of magnitude. Doping methods using liquid metals have significantly changed the photodiode and piezoelectric device performances, providing a powerful approach to tune optoelectronic device outputs.

Vacancy-triggered and dopant-assisted NO electrocatalytic reduction over MoS2

Nitric oxide electroreduction reaction (NOER) is an efficient method for NH₃ synthesis and NO_x-related pollutant treatment. However, current research on NOER catalysts mainly focuses on noble metals and single atom catalysts, while low-cost transition metal dichalcogenides (TMDCs) are rarely considered. Herein, by applying density functional theory (DFT) calculations, we study the catalytic performance of NOER over 2H-MoS₂ monolayers with the most common S vacancies and some Mo atoms substituted by transition metal atoms (denoted as TM-MoS₂@V_S). Our results show that an S vacancy and a heteroatom substitution tend to form a first nearest neighbour (1NN) pair, which greatly improves the NOER catalytic performance of 2H-MoS₂. The S vacancy site can trigger NOER by strongly adsorbing a NO molecule and elongating the NO bond, while the heteroatom dopant can assist NOER by tuning the electron donating capability of 2H-MoS₂ which breaks the linear scaling relations among key reaction intermediates. At low NO coverage, NH₃ can be correspondingly yielded at -0.06 and -0.38 V onset potentials over the Pt- and Au-doped MoS₂ catalysts with S vacancies (Pt-MoS₂@V_S and Au-MoS₂@V_S). At high NO coverage, N₂O/N₂ is thermodynamically favored. Meanwhile, the competing hydrogen evolution reaction (HER) is suppressed. Thus, the Pt-MoS₂@V_S catalysts are promising candidates for NOER. In addition, coupling the substitutional doping of Mo atoms to S vacancies presents great potential in improving the catalytic activity and selectivity of MoS₂ for other reactions. In general, the strategy of coupling hetero-metal doping and chalcogen vacancy can be extended to enhance the catalytic activity of other TMDCs.