Role of Plasma in Catalyst Preparation and Modification for Oxygen Evolution Reaction

Plasma as a promising solution to catalyst synthesis and modification has received great attention in the field of electrochemical water splitting. However, a comprehensive overview detailing how plasma treatments of catalysts enhance oxygen evolution reaction (OER) performance is currently lacking. Here, we review the advances and challenges in cold plasma for catalyst preparation and modification. We discuss the underlying mechanisms responsible for enhanced OER performance on plasma-treated catalysts, where the surface area, active sites, vacancy type/content, heteroatom doping, etching, and surface functionalization could be mediated. This review aims to provide valuable insights into the role of plasma treatments in advancing OER electrocatalysis for sustainable energy applications.

Self-templated fabrication of P-doped CoMoO4-Co3O4 hollow nanocages for the efficient oxygen evolution reaction

Finding reservoir-rich and efficient electrocatalysts for the alkaline oxygen evolution reaction (OER) is crucial for further sustainable energy development. Despite the advantages of high earth abundance, easy availability, and tunable composition, transition-metal oxides are typically considered poor electrocatalysts for the OER. In this study, a composite P-doped CoMoO4-Co3O4 hollow nanocage is deliberately synthesized through a cation-exchange, pyrolysis, and phosphorization approach using an innovative self-template strategy with ZIF-67 as the sacrificial template. Hollow nanocages provide large surface areas and abundant active sites, enhancing electron transfer. Hybridization with other components increases the number of electrochemically reactive sites and optimizes the advantages of different element components. As a result, the P-CoMoO4-Co3O4 hollow nanocage catalyst demonstrates high OER performance, with an overpotential of 279 mV at a current density of 10 mA cm-2. Additionally, P-CoMoO4-Co3O4 catalysts exhibit good dispersibility and excellent long-term stability. Experimental findings and density functional theory (DFT) calculations indicate that the phosphorus-doping effect in various aspects contributes significantly to the superior catalytic activity of P-CoMoO4-Co3O4. This work provides a valuable method for designing cost-effective P doped Co-based bimetal oxide catalysts with outstanding OER performance for industrial applications.

Nanoengineered Cobalt Electrocatalyst for Alkaline Oxygen Evolution Reaction

The alkaline oxygen evolution reaction (OER) remains a bottleneck in green hydrogen production owing to its slow reaction kinetics and low catalytic efficiencies of earth abundant electrocatalysts in the alkaline OER reaction. This study investigates the OER performance of hierarchically porous cobalt electrocatalysts synthesized using the dynamic hydrogen bubble templating (DHBT) method. Characterization studies revealed that electrocatalysts synthesized under optimized conditions using the DHBT method consisted of cobalt nanosheets, and hierarchical porosity with macropores distributed in a honeycomb network and mesopores distributed between cobalt nanosheets. Moreover, X-ray photoelectron spectroscopy studies revealed the presence of Co(OH)2 as the predominant surface cobalt species while Raman studies revealed the presence of the cubic Co3O4 phase in the synthesized electrocatalysts. The best performing electrocatalyst required only 360 mV of overpotential to initiate a current density of 10 mA cm-2, exhibited a Tafel slope of 37 mV dec-1, and stable OER activity over 24 h. The DHBT method offers a facile, low cost and rapid synthesis approach for preparation for highly efficient cobalt electrocatalysts.

Electronic Modulation of MoS2 Nanosheets by N-Doping for Highly Sensitive NO2 Detection at Room Temperature

Transition metal dichalcogenide (TMD) materials hold great promise for gas sensors working at room temperature (RT). But the low response and slow dynamics derived from pristine TMDs remain a challenge toward their real applications. In this work, we report an efficient N-doping strategy to modulate the electronic structure of MoS2 nanosheets (N-MoS2) to achieve improved detection toward NO2. The effect of N-doping on the sensor properties, which has been rarely investigated, is elucidated by both experimental and computational studies. Due to N-doping, the Fermi level of N-MoS2 decreased from -5.29 to -5.33 eV and the band gap was reduced from 1.79 to 1.65 eV. The smaller band gap indicated the reduced resistance of N-MoS2 compared to that of original MoS2. As a result, the response of the MoS2 sensor to 10 ppm of NO2 was improved from 1.23 to 2.31 at RT. The sensor also has a limit of detection (LOD) of 62.5 ppb. To explain the effect of N-doping, density functional theory (DFT) calculations were conducted to figure out the important roles played by N-doping. This work demonstrates a pathway to modulate the chemical and electronic structures of TMD materials for advanced sensors.

Structure and oxygen vacancy engineered CuCo-layered double oxide nanotube arrays as advanced bifunctional electrocatalysts for overall water splitting

In recent years, as a green renewable energy production technology, electrochemical water splitting has demonstrated high development potential. Many materials have been reported as successful catalysts in the water-splitting field. However, it is still a huge challenge to produce bifunctional electrocatalysts for the efficient and sustainable generation of hydrogen and oxygen simultaneously. Herein, we successfully developed oxygen vacancies abundant CuCo layered double oxide (O_v-CuCo-LDO) hollow nanotube arrays (HNTAs) loaded on nickel foam as advanced electrocatalysts for total water splitting. When the current density was 10 mA cm^-2, the O_v-CuCo-LDO HNTAs exhibited outstanding onset overpotentials of 53.9 and 72.5 mV for the hydrogen evolution and oxygen evolution reactions (HER and OER) in alkaline medium, respectively, because of the bimetallic synergistic effect between the cobalt and copper and the unique hollow porous structure. In addition, an as-assembled O_v-CuCo-LDO||O_v-CuCo-LDO electrolytic cell showed a small potential of 1.55 V to deliver a current density of 10 mA cm^-2. Moreover, it also showed remarkable durability after long-term overall water splitting for more than 20 h. The research results in this paper are of great interest to practical applications of the water decomposition process, providing clear and in-depth insights into preliminary robust and efficient multifunctional electrocatalysts for overall water splitting.

Recent Advancements in Chalcogenides for Electrochemical Energy Storage Applications

Energy storage has become increasingly important as a study area in recent decades. A growing number of academics are focusing their attention on developing and researching innovative materials for use in energy storage systems to promote sustainable development goals. This is due to the finite supply of traditional energy sources, such as oil, coal, and natural gas, and escalating regional tensions. Because of these issues, sustainable renewable energy sources have been touted as an alternative to nonrenewable fuels. Deployment of renewable energy sources requires efficient and reliable energy storage devices due to their intermittent nature. High-performance electrochemical energy storage technologies with high power and energy densities are heralded to be the next-generation storage devices. Transition metal chalcogenides (TMCs) have sparked interest among electrode materials because of their intriguing electrochemical properties. Researchers have revealed a variety of modifications to improve their electrochemical performance in energy storage. However, a stronger link between the type of change and the resulting electrochemical performance is still desired. This review examines the synthesis of chalcogenides for electrochemical energy storage devices, their limitations, and the importance of the modification method, followed by a detailed discussion of several modification procedures and how they have helped to improve their electrochemical performance. We also discussed chalcogenides and their composites in batteries and supercapacitors applications. Furthermore, this review discusses the subject’s current challenges as well as potential future opportunities.

Plasma-Assisted Controllable Doping of Nitrogen into MoS2 Nanosheets as Efficient Nanozymes with Enhanced Peroxidase-Like Catalysis Activity

Heteroatom doping is one of the effective ways to improve the catalytic performances of nanozymes. In the present work, the plasma-assisted controllable doping of nitrogen (N) into MoS₂ nanosheets has been initially proposed, resulting in efficient nanozymes. The so-obtained nanozymes were characterized separately by TEM, XRD, XPS, and FTIR. It was discovered that the resulting N-doped MoS₂ nanosheets could present dramatically enhanced peroxidase-like catalytic activities depending on the plasma treatment time. Particularly, that with the 2-min treatment could display the highest catalytic activity, which is over 3-fold higher than that of pristine MoS₂, that was also demonstrated by the kinetics studies. Herein, the N₂ plasma treatment could facilitate the N elements to be doped covalently into MoS₂ nanosheets to achieve the increased surface wettability and affinity of nanozymes for the improved access of the electrons and substrates of catalytic reactions. More importantly, the covalent doping of N elements into MoS₂ nanosheets with a lower Fermi level, as evidenced by the DFT analysis, could facilitate the promoted electron transferring, resulting in the enhanced catalysis of N-doped MoS₂ nanozymes, in addition to the high catalytic stability in water. Such a controllable plasma treatment strategy may open a new door toward the large-scale applications for doping heteroatoms into various nanozymes with improved catalysis performances.

Electrochemical Transformation of Facet-Controlled BiOI into Mesoporous Bismuth Nanosheets for Selective Electrocatalytic Reduction of CO2 to Formic Acid

Mesoporous bismuth nanosheets are prepared through electrochemical transformation of (100)-facet exposed BiOI. Theoretical modeling and calculations are used to simulate the in situ morphological transformation of BiOI into Bi. Mesoporous Bi nanosheets show superior electrochemical CO₂ reduction performance. A faradaic efficiency of 95.9 % at -0.77 V_RHE for the conversion of CO₂ into formic acid, is achieved for the mesoporous Bi nanosheet catalyst compared with 93.8 % at -0.87 V_RHE for the smooth Bi nanosheets. Tafel analysis and DFT calculations indicate that the electrochemical CO₂ reduction on mesoporous Bi nanosheets is kinetically faster with a higher resistance to H₂ generation than that on smooth Bi(001) nanosheets. The CO₂ -to-HCOOH pathway is preferred through formation of an *OCHO intermediate on the (012) and (001) planes of Bi. The mesoporous structure induces a more accessible interaction with CO₂ , which makes a predominant contribution to the enhanced performance compared with the subsequent CO₂ activation on different facets of Bi.