Recent Progress of Vacancy Engineering for Electrochemical Energy Conversion Related Applications

Diversified electrochemical energy storage systems highly depend on electrode material construction. In this area, single-atom catalysts intentionally incorporated within two-dimensional (2D) matrices (SAs@2D) can offer desirable advantages derived from host–guest interactions with abundant extrinsic defects. Nevertheless, the intrinsic manipulation mechanisms and guiding insights regarding the use of SAs@2D in various energy storage devices have not been comprehensively appraised. Firstly, newly updated synthesis methodologies and structure–activity mechanisms are summarized in this review. Then, cutting-edge applications regarding the use of SAs@2D hybrids in various rechargeable batteries, such as Li–O2, Li–CO2, Li–S, Li–metal, and Zn–air batteries, and the central kinetics amelioration schemes underlying these applications are highlighted in detail for the first time. We argue that the maximally exposed active centers and optimized electronic environments are responsible for enhancing mass transfer throughout the conductive grid, which is indispensable for accelerating the redox kinetics and enhancing energy efficiencies in advanced battery systems. In particular, in-depth mechanisms describing how high-density unsaturated coordination sites can tune the adsorption-nucleation-growth behaviors of intermediates in the framework and how the impressive electronic and structural characteristics of SAs@2D can lower potential energy barriers during redox reactions are fundamentally concentrated on. Finally, challenges and advisory guidelines for further investigations relating to the use of SAs@2D in rechargeable batteries are presented.

Two-dimensional matrices confining metal single atoms with enhanced electrochemical reaction kinetics for energy storage applications

The transformation of biomass to graphene has recently attracted increasing attention because of its high carbon contents and renewable nature. Various applications of biomass-derived graphene are currently sought because of its potential cost-effective, large-scale, quality-controllable production in an eco-friendly manner. In comparison to traditional synthesis of graphene, the transformation of biomass to graphene involves a mix of “top to down” and “bottom to up” processes, in which the biomass is decomposed into carbon fragments, followed by their growth through specific rearrangements into graphene. This critical review discusses merits and limitations of various synthesis methods (e.g., hydrothermal carbonization, pyrolysis, plasma, Joule heating and laser irradiation) of biomass-derived graphene. The role of biomass precursors, chemical additives and operating temperatures in the transformation of biomass to graphene with desired characteristics is delineated. Insights into mechanisms involved in the conversion of biomass to graphene products are provided for each specific type of biomass precursors. Emerging energy and environmental applications of biomass-derived graphene are summarized based on its specific physicochemical properties. This review concludes with an overview of current knowledge gaps and proposes future research directions for advancing the large-scale production of biomass-derived graphene for attractive and practical applications in the fields of energy and environment.

Synthesis, formation mechanisms and applications of biomass-derived carbonaceous materials: a critical review

Scalable synthesis of Fe3N nanoparticles within N-doped carbon frameworks as efficient electrocatalysts for oxygen reduction reaction.

Supported metal nanostructures are the most extensively studied heterogeneous catalysts, benefiting from easy separation, regeneration and affordable cost. The size of the supported metal species is one of the decisive factors in determining the activity of heterogeneous catalysts. Particularly, the unsaturated coordination environment of metal atoms preferably act as the active centers, minimizing these metal species can significantly boost the specific activity of every single metal atom. Single-atom catalysts/catalysis (SACs), containing isolated metals atomically dispersed on or coordinated with the surface of a support material, represent the ultimate utilization of supported metals and maximize metal usage efficiency. Graphene, a two-dimensional star material, exhibiting extraordinary physical and chemical properties, has been approved as an excellent platform for constructing SACs. When atomically dispersed metal atoms are strongly anchored on the graphene surface, featuring ultra-high surface area and excellent electronic properties, SACs offer a great potential to significantly innovate the conventional heterogeneous catalysis, especially in the field of electrocatalysis. In this review, a detailed discussion of graphene-supported SACs, including preparation approaches, characterization techniques and applications on typical electrocatalytic reactions is provided. The advantages and unique features of graphene-supported SACs as efficient electrocatalysts and the upcoming challenges for improving their performance and further practical applications are also highlighted.

Graphene-supported single-atom catalysts and applications in electrocatalysis.

Cost-effective preparation of efficient electrocatalysts is vitally important for energy storage and conversion. Here, a facile chemical activation strategy using biomass cellulose as the carbon feedstock to fabricate isolated Fe atoms dispersed on a nitrogen doped graphene/nanocarbon hybrid is reported. This new single atom catalyst aFe-NGC worked as an excellent electrocatalyst towards the ORR compared to commercial Pt/C with 30 mV higher positive half-wave potential, larger current density, better stability and stronger methanol-tolerance. The key active sites for enhancing the ORR activity originated from the constructed high loading Fe–N/C configuration coupled with doped nitrogens, as explored by optimizing the activation temperatures and characterized by state-of-the-art techniques including aberration-corrected STEM and synchrotron XANES. This strategy could be developed into a general approach to prepare highly efficient atomic metal electrocatalysts using abundant biomass as a cost-effective carbon source.

Isolated Fe atoms dispersed on cellulose-derived nanocarbons as an efficient electrocatalyst for the oxygen reduction reaction.

Formation and influence of graphene in Inconel 625 prepared by selective laser melting

In this study, seven 316L stainless steel (316L SS) bulks with different angles (0°, 15°, 30°, 45°, 60°, 75°, and 90°) relative to a build substrate were built via selective laser melting (SLM). The influences of different angles on the metallography, microstructure evolution, tensile properties, and corrosion resistance of 316L SS were studied. The 0° sample showed the morphology of corrugated columnar grains, while the 90° sample exhibited equiaxed grains but with a strong texture. The 60° sample had a good strength and plasticity: the tensile strength with 708 MPa, the yield strength with 588 MPa, and the elongation with 54.51%. The dislocation strengthening and grain refinement play a vital role in the mechanical properties for different anisotropy of the SLM-fabricated 316L SS. The 90° sample had greater toughness and corrosion resistance, owing to the higher volume fraction of low-angle grain boundaries and finer grains.

Jinfang Zhang

Papers

Isolated Fe atoms dispersed on cellulose-derived nanocarbons as an efficient electrocatalyst for the oxygen reduction reaction.

Formation and influence of graphene in Inconel 625 prepared by selective laser melting

Study on Mechanism of Structure Angle on Microstructure and Properties of SLM-Fabricated 316L Stainless Steel.