High-performance nanostructured bio-based carbon electrodes for energy storage applications

Polyacrylonitrile (PAN)-based carbon precursor is a well-established and researched material for electrodes in energy storage applications due to its good physical properties and excellent electrochemical performance. However, in the fight of preserving the environment and pioneering renewable energy sources, environmentally sustainable carbon precursors with superior electrochemical performance are needed. Therefore, bio-based materials are excellent candidates to replace PAN as a carbon precursor. Depending on the design requirement (e.g. carbon morphology, doping level, specific surface area, pore size and volume, and electrochemical performance), the appropriate selection of carbon precursors can be made from a variety of biomass and biowaste materials. This review provides a summary and discussion on the preparation and characterization of the emerging and recent bio-based carbon precursors that can be used as electrodes in energy storage applications. The review is outlined based on the morphology of nanostructures and the precursor's type. Furthermore, the review discusses and summarizes the excellent electrochemical performance of these recent carbon precursors in storage energy applications. Finally, a summary and outlook are also given. All this together portrays the promising role of bio-based carbon electrodes in energy storage applications.

Advanced Biomass-Derived Electrocatalysts for the Oxygen Reduction Reaction

Recent progress in advanced nanostructures synthesized from biomass resources for the oxygen reduction reaction (ORR) is reviewed. The ORR plays a significant role in the performance of numerous energy-conversion devices, including low-temperature hydrogen and alcohol fuel cells, microbial fuel cells, as well as metal-air batteries. The viability of such fuel cells is strongly related to the cost of the electrodes, especially the cathodic ORR electrocatalyst. Hence, inexpensive and abundant plant and animal biomass have become attractive options to obtain electrocatalysts upon conversion into active carbon. Bioresource selection and processing criteria are discussed in light of their influence on the physicochemical properties of the ORR nanostructures. The resulting electrocatalytic activity and durability are introduced and compared to those from conventional Pt/C-based electrocatalysts. These ORR catalysts are also active for oxygen or hydrogen evolution reactions.

Co₃O₄@CoS Core-Shell Nanosheets on Carbon Cloth for High Performance Supercapacitor Electrodes

In this work, a two-step electrodeposition strategy is developed for the synthesis of core-shell Co₃O₄@CoS nanosheet arrays on carbon cloth (CC) for supercapacitor applications. Porous Co₃O₄ nanosheet arrays are first directly grown on CC by electrodeposition, followed by the coating of a thin layer of CoS on the surface of Co₃O₄ nanosheets via the secondary electrodeposition. The morphology control of the ternary composites can be easily achieved by altering the number of cyclic voltammetry (CV) cycles of CoS deposition. Electrochemical performance of the composite electrodes was evaluated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy techniques. The results demonstrate that the Co₃O₄@CoS/CC with 4 CV cycles of CoS deposition possesses the largest specific capacitance 887.5 F·g⁻¹ at a scan rate of 10 mV·s⁻¹ (764.2 F·g⁻¹ at a current density of 1.0 A·g⁻¹), and excellent cycling stability (78.1% capacitance retention) at high current density of 5.0 A·g⁻¹ after 5000 cycles. The porous nanostructures on CC not only provide large accessible surface area for fast ions diffusion, electron transport and efficient utilization of active CoS and Co₃O₄, but also reduce the internal resistance of electrodes, which leads to superior electrochemical performance of Co₃O₄@CoS/CC composite at 4 cycles of CoS deposition.

A facile strategy to fabricate nitrogen-doped graphene aerogel-supported Fe3N nanoparticles as efficient electrocatalysts for the oxygen reduction reaction

In this study, a novel hybrid composed of iron nitride and nitrogen-functionalized graphene aerogel (Fe₃N/N-GA) was fabricated and used as an electrode material for the oxygen reduction reaction (ORR).

Metal-Free and Noble Metal-Free Heteroatom-Doped Nanostructured Carbons as Prospective Sustainable Electrocatalysts

The large-scale deployment of many types of fuel cells and electrolyzers is currently constrained by the lack of sustainable and efficient catalysts that can replace the less earth-abundant, noble metal-based catalysts, which are commonly used in these renewable energy systems. This burgeoning issue has led to explosive research efforts worldwide to find alternative, metal-free and noble metal-free catalysts that are composed of inexpensive and earth-abundant elements. Hence, the recent discoveries that doping carbon nanomaterials with heteroatoms (such as N, S, B, etc.) can give sustainable materials with good electrocatalytic activity for reactions carried out in fuel cells and electrolyzers have been not only quite exciting but also very promising to address these challenging issues. Interestingly, even though they contain no metals or involve only the inexpensive, more earth-abundant ones, the catalytic activity of some of these materials fares well with those of the commercially used noble metal-based electrocatalysts, such as Pt/C. However, research efforts to improve the catalytic activity, selectivity, and stability of some of these materials for various reactions are still necessary and thus continuing. While some of these efforts have focused on finding synthetic methods that can tune the structures and compositions of already known materials and thereby improve their catalytic properties (activity, selectivity, stability, etc.), others have focused on developing entirely new materials that can exhibit better or superior catalytic properties. In these efforts, additional considerations are also being paid to find facile synthetic routes or renewable and inexpensive precursors that can lead to such types of catalysts in order to make the entire process highly sustainable and widely applicable. In this Account, notable heteroatom-doped carbon catalysts that have been developed for reactions in fuel cells and water electrolyzers, the various synthetic procedures employed to make them, and the challenges involved in their synthesis as well as their characterizations are discussed. The methods used to systematically vary the structures and compositions of the precursors of these materials, as well as the materials themselves, and the different experimental, imaging, and spectroscopic methods used to investigate the properties and structure-property relationships of the materials for various energy related reactions are also included. The discussions focus mainly around the recent notable results reported on these materials by the author's and other research groups worldwide, albeit not exhaustively. Finally, the author's perspective about the challenges remaining in the field that need to be addressed, the many existing unanswered questions that beg for more research, and the future prospects for research related to the above topics are also mentioned.

Facile morphology controlled synthesis of nanostructured Co3O4 films on nickel foam and their pseudocapacitive performance

The as-synthesized 3D hierarchically porous Co₃O₄ network film on nickel foam shows prominent pseudocapacitive performance.

Sucrose-derived activated carbons: electron transfer properties and application as oxygen reduction electrocatalysts

ORR electrocatalysts derived from sugar: activated carbons derived from sucrose showed electrocatalytic activity for the oxygen reduction reaction.

Controllable hydrothermal-assisted synthesis of mesoporous Co3O4nanosheets

Mesoporous Co₃O₄nanosheets were fabricated through a simple hydrothermal process with subsequent heat treatment. The results of capacitive characteristics clarify the mesoporous Co₃O₄nanosheets have potential applications in supercapacitors.