Abstract
Copper hollow fibers were prepared via dry-wet spinning of a polymer solution of N-methylpyrrolidone, Polyetherimide, Polyvinyl Pyrolidone, and copper particles of sizes in the range of 1–2 µm. To remove template molecules and to sinter the copper particles, the time of calcination was varied in a range of 1–4 h at 600 °C. This calcination temperature was determined based on Thermal Gravimetric Analysis (TGA), showing completion of hydrocarbon removal at this temperature. Furthermore, the temperature of the subsequent treatment of the fibers in a flow of 4% H2 (in Ar) was varied in the range of 200 °C to 400 °C, at a fixed time of 1 h. Temperature programmed reduction experiments (TPR) were used to analyze the hydrogen treatment. The Faradaic Efficiency (FE) towards CO in electrochemical reduction of CO2 was determined at −0.45 V vs. RHE (Reversible Hydrogen Electrode), using a 0.3 M KHCO3 electrolyte. A calcination time of 3 h at 600 °C and a hydrogen treatment temperature of 280 °C were found to induce the highest FE to CO of 73% at these constant electrochemical conditions. Optimizing oxidation properties is discussed to likely affect porosity, favoring the CO2 gas distribution over the length of the fiber, and hence the CO2 reduction efficiency. Treatment in H2 in the range of 250 to 300 °C is proposed to affect the content of residual (subsurface) oxygen in Cu, which leads to favorable properties on the nanoscale.
Highlights
Published: 29 April 2021The penetration of renewable electricity into the chemical industry provides potential for the development of electrochemical synthesis and storage methods [1,2]
The trends we show in Figure for the CO, generally are mirrored by the of hydrogen
We studied the effect of calcination time (1–4 h at 600 ◦ C), and temperature of treatment in hydrogen (200–400 ◦ C in 4 vol-% H2 in Ar) on the performance of copper hollow fibers in the electroreduction of CO2 to produce CO
Summary
Published: 29 April 2021The penetration of renewable electricity into the chemical industry provides potential for the development of electrochemical synthesis and storage methods [1,2]. To obtain high current densities for reduction of CO2 , mass transfer of CO2 to the electrode surface should be optimized. Sargent and coworkers reported an electrode composition allowing very high Faradaic Efficiency towards ethylene [12]. In such gas diffusion configuration, CO2 is flown by the catalyst-electrolyte-interface, collecting gas phase products of reaction in the gas-flow. Some of us have recently reported the design of copper hollow fiber electrodes [13], which provide high mass-transfer rates per volume, but by a flow-through configuration [14]. Copper hollow fiber electrodes demonstrate excellent Faradaic Efficiency in conversion of CO2 to CO at optimized applied potential [13]
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