Huawei Zhang

Toward Aerogel Electrodes of Superior Rate Performance in Supercapacitors through Engineered Hollow Nanoparticles of NiCo2O4

Abstract A biomass‐templated pathway is developed for scalable synthesis of NiCo2O4@carbon aerogel electrodes for supercapacitors, where NiCo2O4 hollow nanoparticles with an average outer diameter of 30–40 nm are conjoined by graphitic carbon forming a 3D aerogel structure. This kind of NiCo2O4 aerogel structure shows large specific surface area (167.8 m2 g−1), high specific capacitance (903.2 F g−1 at a current density of 1 A g−1), outstanding rate performance (96.2% capacity retention from 1 to 10 A g−1), and excellent cycling stability (nearly without capacitance loss after 3000 cycles at 10 A g−1). The unique structure of the 3D hollow aerogel synergistically contributes to the high performance. For instance, the 3D interconnected porous structure of the aerogel is beneficial for electrolyte ion diffusion and for shortening the electron transport pathways, and thus can improve the rate performance. The conductive carbon joint greatly enhances the specific capacity, and the hollow structure prohibits the volume changes during the charge–discharge process to significantly improve the cycling stability. This work represents a giant step toward the preparation of high‐performance commercial supercapacitors.

Boosting hydrogen evolution via optimized hydrogen adsorption at the interface of CoP3 and Ni2P

Transition metal phosphides (TMPs) have emerged as highly active catalysts for the hydrogen evolution reaction (HER). Herein, we report a novel excellent CoP3/Ni2P catalyst for the HER with a small onset potential of 51 mV vs. RHE, a low Tafel slope of 49 mV dec−1, a small over-potential value of 115 mV at 10 mA cm−2, and outstanding long-term stability. The normalized polarization curve also shows that CoP3/Ni2P has the best intrinsic catalytic activity compared to pure CoP3 and pure Ni2P. Density functional theory (DFT) calculations reveal that the remarkably enhanced catalytic activity is due to the interface effect of CoP3/Ni2P. The strong interactions at the interface can optimize the electronic environment around the active sites, leading to suitable H+ adsorption and H2 formation kinetics and energetics, thereby enhancing the catalytic activity.

Photogenerated-carrier separation along edge dislocation of WO3 single-crystal nanoflower photoanode

Point defects, such as oxygen vacancies in semiconductors, have been widely proven to influence the separation and transfer processes of the photogenerated hot charges. Besides point defects, to date, scarcely any study has focused on expounding the functions of line defects (such as dislocations) in the crystal of semiconductor photoanodes and influencing the photogenerated hot charge separation process. Herein, a nanoflower (NF)-like WO3 single-crystal thin film photoanode with edge dislocations is reported. The dislocation induces mismatch of the (002) and (020) facets. Further photoelectrochemical (PEC) performance and DOS calculation results indicate that a heterojunction system could be formed along the edge dislocations due to the energy difference between the mismatched (002) and (020) facets. Therefore, this present study provides an understanding of the line defect in the photogenerated hot carrier separation process and a novel method to improve the properties of photoelectrodes and photocatalytic materials in the near future.

Sub-1.5 nm Ultrathin CoP Nanosheet Aerogel: Efficient Electrocatalyst for Hydrogen Evolution Reaction at All pH Values

Transition metal phosphides (TMPs) are certified high performance electrocatalysts for the hydrogen evolution reaction (HER). The ultrathin 2D structure of TMPs can offer abundant adsorption sites to boost HER performance. Herein, an ice-templating strategy is developed to prepare CoP aerogels composed of 2D ultrathin CoP nanosheets (<1.5 nm) using sustainable alginate biomass (seaweed extract) as the precursor. The highly porous aerogel structure can not only deliver facile mass transfer, but also prevent aggregation of the nanosheets into layered structures. As expected, the obtained CoP nanosheet aerogels exhibit remarkable stability and excellent electrocatalytic HER performance at all pH values. For instance, the sample CoP-400 presents a low overpotential of 113, 154, and 161 mV versus RHE at a current density of 10 mA cm-2 in 0.5 m H2SO4, 1 m KOH, and 1 m phosphate buffer solution, respectively. In addition, CoP-400 displays low Tafel slopes at all pH values due to the interconnected highly porous structure of the aerogel, indicating that the sample can provide low-resistance channels for mass transport. Density functional theory calculations reveal that P-top and Co bridge on (011) facet of CoP are more favorable sites during the process of HER in acid and alkaline solutions, respectively.