[Abstract unavailable

Two-dimensional (2D) materials and ultrathin nanosheets are advantageous for elevating the catalysis performance and elucidating the catalysis mechanism of heterogeneous catalysts, but they are mostly restricted to inorganic or organic materials based on covalent bonds. We report an electrochemical/chemical exfoliation strategy for synthesizing metal-organic 2D materials based on coordination bonds. A catechol functionalized ligand is used as the redox active pillar to construct a pillared-layer framework. When the 3D pillared-layer MOF serves as an electrocatalyst for water oxidation (pH 13), the pillar ligands can be oxidized in situ and removed. The remaining ultrathin (2 nm) nanosheets of the metal-organic layers are an efficient catalyst with overpotentials as low as 211 mV at 10 mA cm and a turnover frequency as high as 30 s at an overpotential of 300 mV.

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.

In this paper, we reported an effective and simple strategy to prepare large areal mass loading of MnO2 on porous graphene gel/Ni foam (denoted as MnO2/G-gel/NF) for supercapacitors (SCs). The MnO2/G-gel/NF (MnO2 mass: 13.6 mg cm(-2)) delivered a large areal capacitance of 3.18 F cm(-2) (234.2 F g(-1)) and good rate capability. The prominent electrochemical properties of MnO2/G-gel/NF are attributed to the enhanced conductivities and improved accessible area for ions in electrolytes. Moreover, an asymmetric supercapacitor (ASC) based on MnO2/G-gel/NF (MnO2 mass: 6.1 mg cm(-2)) as the positive electrode and G-gel/NF as the negative electrode achieved a remarkable energy density of 0.72 mW h cm(-3). Additionally, the fabricated ASC device also exhibited excellent cycling stability, with less than 1.5% decay after 10,000 cycles. The ability to effectively develop SC electrodes with high mass loading should open up new opportunities for SCs with high areal capacitance and high energy density.

Realizing fast charging–discharging for high mass loading pseudocapacitive materials has been a great challenge in the field of supercapacitors because of the sluggish electron and ion migration kinetics through the thick electrode materials. Here we demonstrate for the first time a facile hydrothermal treatment that can substantially enhance the rate capability of a highly loaded manganese oxide electrode via the Ostwald ripening process. Hydrothermal treatment improves not only the electrical conductivity of manganese oxide but also the ion diffusion rate in the thick oxide film. At slow scan rates below 40 mV s–1, the capacitance of the hydrothermally treated manganese oxide electrode increases linearly with mass loading (up to 23.5 mg cm–2) as expected for a capacitor under the non-diffusion-limited conditions. At high scan rates beyond 100 mV s–1, capacitive saturation is observed only at a high mass loading of ∼9 mg cm–2, which is significantly greater than the values reported for other manganese oxide electrodes. The electrode achieves an areal capacitance of 618 mF cm–2 at a high scan rate of 200 mV s–1, which is 3 times greater than that of the untreated sample. An asymmetric supercapacitor assembled with a hydrothermally treated manganese oxide cathode and a vanadium oxide/exfoliated carbon cloth anode can deliver a good volumetric energy density of 5 mWh cm–3. This value is 2–10 times greater than the values obtained from supercapacitors with comparable dimensions.