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Electrocatalytic reduction of CO2 to a single product at high current densities and efficiencies remains a challenge. However, the conventional electrode preparation methods, such as drop-casting, usually suffer from low intrinsic activity. Herein, we report a synthesis strategy for preparing heterogeneous electrocatalyst composed of 3D hierarchical Cu dendrites that derived from an in situ electrosynthesized hollow copper metal-organic framework (MOF), for which the preparation of the Cu-MOF film took only 5 min. The synthesis strategy preferentially exposes active sites, which favor's the reduction of CO2 to formate. The current density could be as high as 102.1 mA cm-2 with a selectivity of 98.2 % in ionic-liquid-based electrolyte and a commonly used H-type cell.

Syngas (CO/H2 ) is a feedstock for the production of a variety of valuable chemicals and liquid fuels, and CO2 electrochemical reduction to syngas is very promising. However, the production of syngas with high efficiency is difficult. Herein, we show that defective indium selenide synthesized by an electrosynthesis method on carbon paper (γ-In2 Se3 /CP) is an extremely efficient electrocatalyst for this reaction. CO and H2 were the only products and the CO/H2 ratio could be tuned in a wide range by changing the applied potential or the composition of the electrolyte. In particular, using nanoflower-like γ-In2 Se3 /CP (F-γ-In2 Se3 /CP) as the electrode, the current density could be as high as 90.1 mA cm-2 at a CO/H2 ratio of 1:1. In addition, the Faradaic efficiency of CO could reach 96.5 % with a current density of 55.3 mA cm-2 at a very low overpotential of 220 mV. The outstanding electrocatalytic performance of F-γ-In2 Se3 /CP can be attributed to its defect-rich 3D structure and good contact with the CP substrate.

Electrochemical reduction of CO2 to CH3 OH is of great interest. Aerogels have fine inorganic superstructure with high porosity and are known to be exceptional materials. Now a Pd-Cu bimetallic aerogel electrocatalyst has been developed for conversion of CO2 into CH3 OH. The current density and Faradaic efficiency of CH3 OH can be as high as 31.8 mA cm-2 and 80.0 % over the Pd83 Cu17 aerogel at a very low overpotential (0.24 V). The superior performance of the electrocatalyst results from efficient adsorption and stabilization of the CO2 radical anion, high Pd0 /PdII and CuI +Cu0 /CuII ratios, and sufficient Pd/Cu grain boundaries of aerogel nanochains.