Electrochemical Oxidation of Methane to Methanol on Electrodeposited Transition Metal Oxides.

Electrochemical partial oxidation of methane to methanol is a promising approach to the transformation of stranded methane resources into a high-value, easy-to-transport fuel or chemical. Transition metal oxides are potential electrocatalysts for this transformation. However, a comprehensive and systematic study of the dependence of methane activation rates and methanol selectivity on catalyst morphology and experimental operating parameters has not been realized. Here, we describe an electrochemical method for the deposition of a family of thin-film transition metal (oxy)hydroxides as catalysts for the partial oxidation of methane. CoOx, NiOx, MnOx, and CuOx are discovered to be active for the partial oxidation of methane to methanol. Taking CoOx as a prototypical methane partial oxidation electrocatalyst, we systematically study the dependence of activity and methanol selectivity on catalyst film thickness, overpotential, temperature, and electrochemical cell hydrodynamics. Optimal conditions of low catalyst film thickness, intermediate overpotentials, intermediate temperatures, and fast methanol transport are identified to favor methanol selectivity. Through a combination of control experiments and DFT calculations, we show that the oxidized form of the as-deposited (oxy)hydroxide catalyst films are active for the thermal oxidation of methane to methanol even without the application of bias potential, demonstrating that high valence transition metal oxides are intrinsically active for the activation and oxidation of methane to methanol at ambient temperatures. Calculations uncover that electrocatalytic oxidation enables reaching an optimum potential window in which methane activation forming methanol and methanol desorption are both thermodynamically favorable, methanol desorption being favored by competitive adsorption with hydroxide anion.

Amorphous mesoporous GeO x anode for Na-ion batteries with high capacity and long lifespan.

It is recently demonstrated that amorphous Ge anode shows higher reversible Na-ion storage capacity (590 mA h g-1) than crystallized Ge anode (369 mA h g-1). Here, amorphous GeO x anode is prepared by a simple wet-chemistry reduction route at room temperature. The obtained amorphous GeO x shows a porous hierarchical architecture, accompanied with a Brunauer-Emmett-Teller surface area of 159 m2 g-1 and an average pore diameter of 14 nm. This unique structure enables the GeO x anode to enhance the Na-ion/electron diffusion rate, and buffer the volume change. As anode for Na-ion battery, high reversible capacity over 400 mA h g-1, fine rate capability with a capacity of 200 mA h g-1 maintained at 3.0 A g-1 and long-term cycling stability with 270 mA h g-1 even over 1000 cycles at 1.0 A g-1 are obtained.