Ligand leaching enabling improved electrocatalytic oxygen evolution performance.

Design and fabrication of cost-effective (pre-)catalysts are important for water splitting and metal-air batteries. In this direction, various metal-organic frameworks (MOFs) have been investigated as pre-catalysts for oxygen evolution. However, the activation process and the complex reconstruction behaviour of these MOFs are not well understood. Herein, square-like MOF nanosheets in which carbon nanotubes were embedded were prepared by introducing an amine ligand to coordinate with Ni ions and then reacting with [Fe(CN)6]3-. The formed MOF nanosheets containing nickel and iron species were then activated by NaBH4, inducing the leaching of ligands and the formation of tiny active species in situ loaded on carbon nanotubes. The prepared catalyst shows superior oxygen evolution performance with an ultralow overpotential of 231 mV for 10 mA cm-2, a fast reaction kinetics with a small Tafel slope of 52.3 mV dec-1, and outstanding catalysis stability. The excellent electrocatalytic performance for oxygen evolution can be attributed to the structural advantage of in situ derived small sized active species and one-dimensional conductive networks. This work provides a new thought for the enhancement of the electrocatalytic performance of MOF materials.

N-Doped Carbon as a Promoted Substrate for Ir Nanoclusters toward Hydrogen Oxidation in Alkaline Electrolytes.

Development of effective electrocatalysts toward hydrogen oxidation with a low content of noble metals has attracted the attention of the catalytic community. In this work, a novel catalyst composed of nitrogen-doped carbon acting as the substrate and Ir nanoclusters as active species was prepared, which was then employed as an effective catalyst for the hydrogen oxidation reaction (HOR) in an alkaline electrolyte. In 0.1 M KOH, the optimized catalyst provides an exchange current density of 0.144 mA cmIr-2 for HOR that outperforms the catalytic activity of the commercial Pt/C catalyst with a Pt content of 20 wt %. The substrate induces highly active Ir sites that markedly boosted the electrocatalytic activity for HOR. The nitrogen-doped carbon substrate increases the stability of Ir nanoclusters and decreases the absorption energy of hydrogen on Ir sites; at the same time, the higher electrostatic potential around the adsorbed hydrogen on Ir/N-doped carbon also enables them to be easily attracted by OH- species, both of which enhanced the catalytic activity. The excellent catalytic activity and the understanding shown here will give some hints for the development of HOR catalysts used in alkaline electrolytes.