Li-ion batteries have contributed to the commercial success of portable electronics and may soon dominate the electric
transportation market provided that major scientific advances including new materials and concepts are developed. Classical
positive electrodes for Li-ion technology operate mainly through an insertion–deinsertion redox process involving cationic
species. However, this mechanism is insufficient to account for the high capacities exhibited by the new generation of Li-rich
(Li1CxNiyCozMn(1

Reversible anionic redox chemistry inhigh-capacity layered-oxide electrodes

Tailoring of electrocatalyst interactions at interfacial level to benchmark the oxygen reduction reaction

MoS2||CoP heterostructure loaded on N, P-doped carbon as an efficient trifunctional catalyst for oxygen reduction, oxygen evolution, and hydrogen evolution reaction

High-efficiency utilization of CO2 facilitates the reduction of CO2 concentration in the global atmosphere and hence the alleviation of the greenhouse effect. The catalytic hydrogenation of CO2 to produce value-added chemicals exhibits attractive prospects by potentially building energy recycling loops. Particularly, methanol is one of the practically important objective products, and the catalytic hydrogenation of CO2 to synthesize methanol has been extensively studied. In this review, we focus on some basic concepts on CO2 activation, the recent research advances in the catalytic hydrogenation of CO2 to methanol, the development of high-performance catalysts, and microscopic insight into the reaction mechanisms. Finally, some thinking on the present research and possible future trend is presented.

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Catalytic Hydrogenation of CO2 to Methanol: A Review

Exploring low-cost, highly active, and durable oxygen reduction catalysts is essential for the widespread use of proton exchange membrane fuel cells. Fe–N–C catalysts with nitrogen-coordinated single-atom (Fe–Nx) active sites are the most promising candidates due to their highest activity in acid media among platinum-group-metal-free catalysts. However, the application of Fe–N–C catalysts in realistic fuel cells is still hindered by the conundrum of insufficient stability. This review focuses on the understanding of the structure–stability relationship of Fe–N–C catalysts, which provides valuable guidance for the rational material design toward improved stability. The most significant achievements in recent years are the discovery of several site-specific degradation mechanisms and the identification of intrinsically stable active sites. The development of Fe-free single-atom catalysts is also discussed as an alternative solution. 

Exploring Durable Single-Atom Catalysts for Proton Exchange Membrane Fuel Cells

The highly efficient energy conversion of the polymer-electrolyte-membrane fuel cell (PEMFC) is extremely limited by the sluggish oxygen reduction reaction (ORR) kinetics and poor electrochemical stability of catalysts. Hitherto, to replace costly Pt-based catalysts, non-noble-metal ORR catalysts are developed, among which transition metal-heteroatoms-carbon (TM-H-C) materials present great potential for industrial applications due to their outstanding catalytic activity and low expense. However, their poor stability during testing in a two-electrode system and their high complexity have become a big barrier for commercial applications. Thus, herein, to simplify the research, the typical Fe-N-C material with the relatively simple constitution and structure, is selected as a model catalyst for TM-H-C to explore and improve the stability of such a kind of catalysts. Then, different types of active sites (centers) and coordination in Fe-N-C are systematically summarized and discussed, and the possible attenuation mechanism and strategies are analyzed. Finally, some challenges faced by such catalysts and their prospects are proposed to shed some light on the future development trend of TM-H-C materials for advanced ORR catalysis.

Stabilizing Fe-N-C Catalysts as Model for Oxygen Reduction Reaction.

Rational design and construction of high-efficiency bifunctional catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is crucial for large-scale hydrogen production by water splitting. Herein, by a self-sacrificial template method, Fe–Co–P multi-heterostructure arrays consisting of CoP, Co2P and FeP are built for water splitting. Such multi-heterostructures adjust the local electronic structure and then improve adsorption of reaction intermediates on active sites, which is further proved through density functional theory (DFT) calculations. Thus, without noble metals, the as-prepared Fe–Co–P multi-heterostructure catalyst exhibits very high catalytic performance, which only needs 227 and 87 mV to reach a current density of 20 and 10 mA cm−2 for the OER and HER, respectively, better than most of the related catalysts reported so far. Moreover, when used in alkaline electrolyzers, it delivers a current density of 10 mA cm−2 at a cell voltage of 1.55 V, superior to commercial Pt-group electrodes (1.59 V). Our work offers a novel approach to rationally design catalysts toward water splitting.

Fe–Co–P multi-heterostructure arrays for efficient electrocatalytic water splitting

Compared with three-dimensional (3D) and other materials, two-dimensional (2D) materials with unique properties such as high specific surface area, structurally adjustable band structure, and electromagnetic properties have attracted wide attention. In recent years, great progress has been made for 2D MoS2 in the field of electrocatalysis, and its exposed unsaturated edges are considered to be active sites of electrocatalytic reactions. In this review, we focus on the latest progress of 2D MoS2 in the oxygen reduction reaction (ORR) that has not received much attention. First, the basic properties of 2D MoS2 and its advantages in the ORR are introduced. Then, the synthesis methods of 2D MoS2 are summarized, and specific strategies for optimizing the performance of 2D MoS2 in ORRs, and the challenges and opportunities faced are discussed. Finally, the future of the 2D MoS2-based ORR catalysts is explored.

Two-Dimensional MoS2: Structural Properties, Synthesis Methods, and Regulation Strategies toward Oxygen Reduction.

Synthesis, Modification, and Lithium‐Storage Properties of Spinel LiNi0.5Mn1.5O4

To supress Li/Ni mixing, the strategy of surface modification and Co doping is proposed. Doping trace Co can suppress Li/Ni mixing in the bulk phase of cathode particles, while the rock-salt shell of a cathode originally containing a large amount of Li/Ni mixed rows can be transformed into a cation-ordered spinel phase and a layered phase on the inside by means of surface engineering. Simultaneously, as a coating layer, the Li2MoO4 nanolayer forms on the surface. With the improved Li-ion diffusion, certain inhibitory effects on voltage attenuation and capacity loss are found. It shows that the surface modification with trace Co dopants greatly reduces the Li/Ni mixing level in the material, beneficial to improving the electrochemical performance. As expected, the Li-rich Mn-based cathode material with a low level of overall Li/Ni mixing shows an initial discharging capacity of 303 mAh g-1. This indicates that the joint application of doping and surface coating effectively enhances the performance of the cathode materials with an ultra-low dosage of Co. This idea is helpful to structure other layered cathode materials by surface engineering.

Jingjing Ma

Papers

Stabilizing Fe-N-C Catalysts as Model for Oxygen Reduction Reaction.

Fe–Co–P multi-heterostructure arrays for efficient electrocatalytic water splitting

Two-Dimensional MoS2: Structural Properties, Synthesis Methods, and Regulation Strategies toward Oxygen Reduction.

Synthesis, Modification, and Lithium‐Storage Properties of Spinel LiNi0.5Mn1.5O4

Surface Engineering and Trace Cobalt Doping Suppress Overall Li/Ni Mixing of Li-rich Mn-based Cathode Materials.