The applications of polyoxometalate-functionalized nanocarbon materials (carbon nanotubes or graphene) in electrocatalysis and electrochemical energy conversion and storage as well as in sensor systems are reviewed.
Rechargeable aqueous zinc batteries are promising energy‐storage systems for grid applications. Highly conductive polyaniline (PANI) is a potential cathode, but it tends to deactivate in electrolytes with low acidity (i.e. pH >1) owing to deprotonation of the polymer. In this study, we synthesized a sulfo‐self‐doped PANI electrode by a facile electrochemical copolymerization process. The −SO3− self‐dopant functions as an internal proton reservoir to ensure a highly acidic local environment and facilitate the redox process in the weakly acidic ZnSO4 electrolyte. In a full zinc cell, the self‐doped PANI cathode provided a high capacity of 180 mAh g−1, excellent rate performance of 70 % capacity retention with a 50‐fold current‐density increase, and a long cycle life of over 2000 cycles with coulombic efficiency close to 100 %. Our study opens a door for the use of conducting polymers as cathode materials for high‐performance rechargeable zinc batteries.
Metal oxides have attracted renewed interest as promising electrode materials for high energy density supercapacitors. However, the electrochemical performance of metal oxide materials deteriorates significantly with the increase of mass loading due to their moderate electronic and ionic conductivities. This limits their practical energy. Herein, we perform a morphology and phase-controlled electrodeposition of MnO with ultrahigh mass loading of 10 mg cm on a carbon cloth substrate to achieve high overall capacitance without sacrificing the electrochemical performance. Under optimum conditions, a hierarchical nanostructured architecture was constructed by interconnection of primary two-dimensional ε-MnO nanosheets and secondary one-dimensional α-MnO nanorod arrays. The specific hetero-nanostructures ensure facile ionic and electric transport in the entire electrode and maintain the structure stability during cycling. The hierarchically structured MnO electrode with high mass loading yields an outstanding areal capacitance of 3.04 F cm (or a specific capacitance of 304 F g) at 3 mA cm and an excellent rate capability comparable to those of low mass loading MnO electrodes. Finally, the aqueous and all-solid asymmetric supercapacitors (ASCs) assembled with our MnO cathode exhibit extremely high volumetric energy densities (8.3 mWh cm at the power density of 0.28 W cm for aqueous ASC and 8.0 mWh cm at 0.65 W cm for all-solid ASC), superior to most state-of-the-art supercapacitors.
Paper‐based materials are emerging as a new category of advanced electrodes for flexible energy storage devices, including supercapacitors, Li‐ion batteries, Li‐S batteries, Li‐oxygen batteries. This review summarizes recent advances in the synthesis of paper‐based electrodes, including paper‐supported electrodes and paper‐like electrodes. Their structural features, electrochemical performances and implementation as electrodes for flexible energy storage devices including supercapacitors and batteries are highlighted and compared. Finally, we also discuss the challenges and opportunity of paper‐based electrodes and energy storage devices.
The review offers a comprehensive overview on the synthesis strategies and fundamental understandings of hierarchical porous carbons as supercapacitor electrodes.
NH4+ ions as charge carriers show potential for aqueous rechargeable batteries. Studied here for the first time is the NH4+‐storage chemistry using electrodeposited manganese oxide (MnOx). MnOx experiences morphology and phase transformations during charge/discharge in dilute ammonium acetate (NH4Ac) electrolyte. The NH4Ac concentration plays an important role in NH4+ storage for MnOx. The transformed MnOx with a layered structure delivers a high specific capacity (176 mAh g−1) at a current density of 0.5 A g−1, and exhibits good cycling stability over 10 000 cycles in 0.5 M NH4Ac, outperforming the state‐of‐the‐art NH4+ hosting materials. Experimental results suggest a solid‐solution behavior associated with NH4+ migration in layered MnOx. Spectroscopy studies and theoretical calculations show that the reversible NH4+ insertion/deinsertion is accompanied by hydrogen‐bond formation/breaking between NH4+ and the MnOx layers. These findings provide a new prototype (i.e., layered MnOx) for NH4+‐based energy storage and contributes to the fundamental understanding of the NH4+‐storage mechanism for metal oxides.
High-temperature activation has been commonly used to boost the photoelectrochemical (PEC) performance of hematite nanowires for water oxidation, by inducing Sn diffusion from fluorine-doped tin oxide (FTO) substrate into hematite. Yet, hematite nanowires thermally annealed at high temperature suffer from two major drawbacks that negatively affect their performance. First, the structural deformation reduces light absorption capability of nanowire. Second, this "passive" doping method leads to nonuniform distribution of Sn dopant in nanowire and limits the Sn doping concentration. Both factors impair the electrochemical properties of hematite nanowire. Here we demonstrate a silica encapsulation method that is able to simultaneously retain the hematite nanowire morphology even after high-temperature calcination at 800 °C and improve the concentration and uniformity of dopant distribution along the nanowire growth axis. The capability of retaining nanowire morphology allows tuning the nanowire length for optimal light absorption. Uniform distribution of Sn doping enhances the donor density and charge transport of hematite nanowire. The morphology and doping engineered hematite nanowire photoanode decorated with a cobalt oxide-based oxygen evolution reaction (OER) catalyst achieves an outstanding photocurrent density of 2.2 mA cm at 0.23 V vs Ag/AgCl. This work provides important insights on how the morphology and doping uniformity of hematite photoanodes affect their PEC performance.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.