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A high-performance V4C3TX@NiO-RGO//DRGO asymmetric supercapacitor device is assembled based on a 3D free-standing V4C3TX@NiO-RGO hydrogel as a positive electrode and a 3D DRGO hydrogel as a negative electrode.

Design and engineering of effective electrode catalysts represents a critical first step for hydrogen production by electrochemical water splitting. Nanocomposites based on ruthenium atomically dispersed within a carbon scaffold have emerged as viable candidates. In the present study, ruthenium metal centers are atomically embedded within graphitic carbon nitride/reduced graphene oxide nanosheets by thermal refluxing. Subsequent chemical reduction/oxidation leads to ready manipulation of the ruthenium valence state, as evidenced in microscopic and spectroscopic measurements, and hence enhancement/diminishment of the electrocatalytic activity towards hydrogen evolution reaction in both acidic and alkaline media. This is largely ascribed to the increased/reduced contribution of the Ru valence electrons to the density of state near the Fermi level which dictates the binding and reduction of hydrogen. Results from this study highlight the significance of the valence state of metal centers in the manipulation and optimization of the catalytic performance of single atom catalysts.

Asymmetric supercapacitors (ASCs) based on a battery-type anode and a capacitive-type cathode have been attracting extensive interest because of their high energy density. Herein, NiO nanosheets are hydrothermally deposited onto a V4C3TX substrate, which are then assembled into a 3D porous heterostructure hydrogel through a graphene oxide-assisted self-convergence hydrothermal process at low temperatures. The resultant hierarchical V4C3TX@NiO-reduced graphene oxide (RGO) hydrogel exhibits an ultrahigh specific capacitance up to 1014.5 F g− 1 at 1 A g− 1. Separately, a defective reduced graphene oxide (DRGO) hydrogel is prepared by a cost-effective hydrothermal procedure followed by cobalt-catalyzed gasification, which shows a higher specific capacitance (258 F g− 1 at 1 A g− 1) than untreated RGO hydrogel (176 F g− 1). These two electrodes are then assembled into an ASC, the device features a stable operating voltage of 1.8 V, a maximum energy density of 86.22 Wh kg− 1 at 900 W kg− 1, along with good cycling stability at 96.4% capacitance retention after 10,000 cycles at 10 A g− 1. This work highlights the unique potential of MXenes-based materials for the construction of high-performance ASCs.

Copper compounds have been extensively investigated for diverse applications. However, studies of cuprous hydroxide (CuOH) have been scarce, due to structural metastability. Herein, a facile, wet-chemistry procedure is reported for the preparation of stable CuOH nanostructures via deliberate functionalization with select organic ligands, such as acetylene and mercapto derivatives. The resulting nanostructures are found to exhibit a nanoribbon morphology consisting of small nanocrystals embedded within a largely amorphous nanosheet-like scaffold. The acetylene derivatives are found to anchor onto the CuOH forming Cu-Cࣽ linkages, whereas Cu-S- interfacial bonds are formed with the mercapto ligands. Effective electronic coupling occurs at the ligand-core interface in the former, in contrast to mostly non-conjugated interfacial bonds in the latter, as manifested in spectroscopic measurements and confirmed in theoretical studies based on first principles calculations. Notably, the acetylene-capped CuOH nanostructures exhibit markedly enhanced photodynamic activity in the inhibition of bacteria growth, as compared to the mercapto-capped counterparts, due to a reduced material bandgap and effective photocatalytic generation of reactive oxygen species. Results from this study demonstrate that deliberate structural engineering with select organic ligands is an effective strategy in the stabilization and functionalization of CuOH nanostructures, a critical first step in exploring their diverse applications. This article is protected by copyright. All rights reserved.