No abstract

Commercial supercapacitors using available carbon products have long been criticized for the under-utilization of their prominent specific surface area (SSA). In terms of carbonaceous electrode optimization, excessive improvement in SSA observed in the gaseous atmosphere might have little effect on the final performance because cracked/inaccessible pore alleys considerably block the direct electrolyte ion transport in a practical electrochemical environment. Herein, mesopore-adjustable hierarchically porous carbon nanosheets are fabricated based on a micelle-size-mediated spatial confinement strategy. In this strategy, hydrophobic trimethylbenzene in different volumes of the solvent can mediate the interfacial assembly with a carbon precursor and porogen segment through π–π bonding and van der Waals interaction to yield micelles with good dispersity and the diameter varying from 119 to 30 nm. With an increasing solvent volume, the corresponding diffusion coefficient (3.1–14.3 m2 s–1) of as-obtained smaller micelles increases, which makes adjacent micelles gather rapidly and then grow along the radial direction of oligomer aggregates to eventually form mesopores on hierarchically porous carbon nanosheets (MNC150-4.5). Thanks to the pore-expansion effect of trimethylbenzene, the mesoporous volume can be adjusted from 28.8 to 40.0%. Mesopores on hierarchically porous carbon nanosheets endow MNC150-4.5 with an enhanced electrochemically active surface area of 819.5 m2 g–1, which gives rise to quick electrolyte accessibility and a correspondingly immediate capacitive response of 338 F g–1 at 0.5 A g–1 in a three-electrode system. Electrolyte transport through pathways within MNC150-4.5 ultimately enables the symmetric cell to deliver a high energy output of 50.4 Wh kg–1 at 625 W kg–1 in a 14 m LiOTF electrolyte and 95% capacitance retention after 100,000 cycles, which show its superior electrochemical performance over representative carbon-based supercapacitors with aqueous electrolytes in recent literature.

Copper-based catalysts have shown excellent performance in electrochemical CO 2 reduction, but there has not been much study on copper sulfides. In our work, a simple and low-temperature chemical bath deposition method was used to fabricate CuS nanosheet arrays on brass, on which a Faradaic efficiency over 70% and a production rate over 50 mA•cm −2 for formate were obtained at a low potential of −0.7 V vs RHE when used as a catalytic electrode for CO 2 reduction. During the CO 2 reduction process, CuS nanosheets were partially reduced to Cu 0 and reconstructed to a nanowire network. It was found that residual S beneath the Cu 0 layer lowered the binding energies of intermediates HCOO* and *COOH, promoting their desorption and the successive formation of HCOOH or HCOO − , thus regulating the high selectivity of the product. This work provides a convenient and economical method for developing a highly active electrocatalyst for producing HCOOH in CO 2 electroreduction, and it is beneficial to understand the mechanism of enhanced selectivity to HCOO − for CuS electrode materials.

Electrocatalytic biomass valorization with renewable energy input represents a promising way to produce sustainable and non-fossil-based carbon products. The oxidative production of furandicarboxylic acid (FDCA) from bio-based 5-hydroxymethylfurfural (HMF) has attracted one of the most attention. Herein, spinel CuMn2O4 with an urchin-like nanostructure was synthesized by a hydrothermal method and subsequently soaked in ammonia water to create oxygen vacancies. The as-prepared material was used as an efficient electrocatalyst to oxidize HMF to FDCA. It was confirmed that CuMn2O4 etched with ammonia has an excellent electrocatalytic performance: at a current density of 20 mA/cm2, the potential of HMF oxidation was 1.31 V vs RHE in 1.0 M KOH solution with 10 mM HMF prior to the takeoff of the competing reaction, O2 evolution. Long-term chronoamperometry demonstrated that a 100% conversion of HMF and a 96% Faradaic efficiency of yield of FDCA were achieved. Our results indicated that it is feasible to employ the earth-abundant transition metal-based electrocatalyst CuMn2O4 to selectively oxidize biomass with higher energy conversion efficiency than water splitting as well as to produce valuable products in a H-type electrochemical cell.

High-purity CuS nanosheets have been successfully synthesized at room temperature via a quick, simple, and efficient grinding approach by using CuCl2·2H2O, thiourea, and NaOH as starting materials. The X-ray diffraction (XRD) patterns and Raman spectra indicated that as-prepared CuS was of high purity and scanning electron microscope (SEM) images showed the sheet-like nanostructure. The specific area of as-synthesized CuS nanosheets was obtained with a N2 adsorption/desorption isotherm, and the value is 23.18 m2·g–1, which is higher than that of CuS fabricated by the traditional method. The bandgap of the as-synthesize CuS was calculated to be around 1.8 eV corresponding to the UV–vis diffuse reflection spectra, showing a potential prospect in photocatalysis and solar cells. A 10-g-level production also has been achieved in our laboratory, and the yield was over 95% based on the Cu source. The grinding approach can be a promising method for the industrial-scale production of high-purity CuS nanosheets.