Nitrogen and Sulfur Codoped Graphene Macroassemblies as High-Performance Electrocatalysts for the Oxygen Reduction Reaction in Microbial Fuel Cells

Optimizing the NRR activity of single and double boron atom catalysts using a suitable support: a first principles investigation

Designing cost effective transition-metal free electrocatalysts for nitrogen fixation under ambient conditions is highly appealing from an industrial point of view. Using density functional theory calculations in combination with the computational hydrogen electrode model, we investigate the N2 activation and reduction activity of ten different model catalysts obtained by supporting single and double boron atoms on five different substrates (viz. GaN, graphene, graphyne, MoS2 and g-C3N4). Our results demonstrate that the single/double boron atom catalysts bind favourably on these substrates, leading to a considerable change in the electronic structure of these materials. The N2 binding and activation results reveal that the substrate plays an important role by promoting the charge transfer from the single/double boron atom catalysts to the antibonding orbitals of *N2 to form strong B-N bonds and subsequently activate the inert NN bond. Double boron atom catalysts supported on graphene, MoS2 and g-C3N4 reveal very high binding energies of -2.38, -2.11 and -1.71 eV respectively, whereas single boron atom catalysts supported on graphene and g-C3N4 monolayers bind N2 with very high binding energies of -1.45 and -2.38 eV, respectively. The N2 binding on these catalysts is further explained by means of orbital projected density of states plots which reflect greater overlap between the N2 and B states for the catalysts, which bind N2 strongly. The simulated reaction pathways reveal that the single and double boron atom catalysts supported on g-C3N4 exhibit excellent catalytic activity with very low limiting potentials of -0.67 and -0.36 V, respectively, while simultaneously suppressing the HER. Thus, the current work provides important insights to advance the design of transition-metal free catalysts for electrochemical nitrogen fixation from an electronic structure point of view.

Graphene and biochar-based cathode catalysts for microbial fuel cell: Performance evaluation, economic comparison, environmental and future perspectives

Microbial fuel cells (MFCs) have been the prime focus of research in recent years because of their distinctive feature of concomitantly treating and producing electricity from wastewater. Nevertheless, the electrical performance of MFCs is hindered by a protracted oxygen reduction reaction (ORR), and often a catalyst is required to boost the cathodic reactions. Conventional transition metals-based catalysts are expensive and infeasible for field-scale usage. In this regard, carbon-based electrocatalysts like waste-derived biochar and graphene are used to enhance the commercialisation prospects of MFC technology. These carbon-catalysts possess unique properties like superior electrocatalytic activity, higher surface area, and high porosity conducive to ORR. Theoretically, graphene-based cathode catalysts yield superior results than a biochar-derived catalyst, though at a higher cost. In contrast, the synthesis of waste-extracted biochar is economical; however, its ability to catalyse ORR is debatable. Therefore, this review aims to make a side-by-side techno-economic assessment of biochar and graphene-based cathode catalyst used in MFC to predict the relative performance and typical cost of power recovery. Additionally, the life cycle analysis of the graphene and biochar-based materials has been briefly discussed to comprehend the associated environmental impacts and overall sustainability of these carbo-catalysts.

F127-assisted preparation of FeCo nanoalloys encapsulated in nitrogen-doped carbon for efficient oxygen reduction reaction

A novel F127-assisted ZIF-67 pyrolysis strategy to construct FeCo nanoalloys encapsulated in nitrogen-doped carbon for efficient oxygen reduction reaction was reported.

Sustainable Lignin-Derived Hierarchical Porous Carbon for Supercapacitors: A Novel Approach for Holding Electrochemical Attraction Natural Texture Property of Precursor

Finding low-cost and environmentally friendly precursors that can maintain their electrochemical attraction natural texture properties while obtaining hierarchical porous carbons with high electrochemical performance is desirable for offering a leap forward in industrial applications. However, phenomena associated with the high microporosity of porous carbon remain. Herein, the protective effect of hydrothermal methods and the micropore-forming ability of KOH were used. The as-synthesized porous carbon (PC-1) holds the natural texture property (the retention of texture property with apertures higher than 2 nm was up to 80%) and achieves three-dimensional (3D) architecture with hierarchical structures accompanied by an ultrahigh specific surface area (3559.45 m²/g). Benefiting from its texture properties, PC-1 possesses a high specific capacitance of 288.75 F/g at 0.5 A/g, excellent rate capability as high as 223.72 F/g at 10 A/g, and remarkable conductivity in a three-electrode system with a 6 M KOH electrolyte. In view of its environment friendliness, low cost, and excellent specific capacitance, PC-1 has promising applications in high-performance supercapacitors.