Abstract
AbstractBACKGROUNDThe recycling of CO2by photoelectrochemical reduction has attracted wide interest due to its potential benefits when compared to electro‐ and photo‐catalytic approaches. Among the various available semiconductors, TiO2is the most employed material in photoelectrochemical cells. Besides, Cu is a well‐known electrocatalyst for the production of alcohols from CO2reduction.RESULTSA photoelectrochemical cell consisting of a TiO2‐based membrane electrode assembly (MEA) photoanode and a Cu plate is employed to reduce CO2to methanol and ethanol continuously under UV illumination (100 mW cm−2). A maximum increment of 4.3 mA cm−2in current between the illuminated and dark conditions is achieved at −2 VversusAg/AgCl. The continuous photoelectrochemical reduction process in the filter‐press cell is evaluated in terms of reaction rate (r), as well as Faradaic efficiency (FE) and energy efficiency (EE). At −1.8 VversusAg/AgCl, a maximum reaction rate ofr= 9.5 μmol m−2s−1,FE= 16.2% andEE= 5.2% for methanol andr= 6.8 μmol m−2s−1,FE= 23.2% andEE= 6.8% for ethanol can be achieved.CONCLUSIONSThe potential benefits of the photoanode‐driven system, in terms of yields and efficiencies, are observed when employing a TiO2‐based MEA photoanode and Cu as dark cathode. The results demonstrate first the effect of UV illumination on current density, and then the formation of alcohols from the continuous photoreduction of CO2. Increasing the external applied voltage leads to an enhanced production of methanol, but decreases ethanol formation. The system outperforms previous photoanode‐based systems for CO2‐to‐alcohols reactions. © 2019 Society of Chemical Industry
Highlights
The concentration of CO2 in the atmosphere has increased to worrying levels in recent years, mainly due to fossil fuels burning
The results demonstrate first the effect of UV illumination on current density, and the formation of alcohols from the continuous photoreduction of CO2
Photoelectrochemical behavior of the TiO2 photoelectrode Figure 4a shows the photocurrent response of the TiO2 photoanode Membrane Electrode Assembly (MEA) during on-off illumination cycles in a one-compartment glass under 100 mW·cm-2 of UV illumination at -1.8 V vs. Ag/AgCl in the presence of CO2, while Figure 4b shows the current densities observed with and without illumination in cell when CO2 is continuously bubbling in a potential range between -1.2 V and -2 V vs. Ag/AgCl and a TiO2 loading of 3 mg·cm-2, where an optimal reduction of CO2 to alcohols can be expected. 34, 37, 38
Summary
The concentration of CO2 in the atmosphere has increased to worrying levels in recent years, mainly due to fossil fuels burning. Among the different technologies available, the electrochemical reduction of CO2 has attracted great interest due to the potential economic and environmental benefits This technology, apart from allowing CO2 dissociation at ambient conditions using electricity, is an excellent alternative to store the intermittent energy produced from renewables in the chemical bonds.[2] the integration of a light source in electrochemical reduction devices (a photoelectrochemical approach, PEC) has attracted an increasing interest recently because it may allow avoiding the interconnections between devices, reducing, in principal, system capital costs and electricity losses.[3] Compared to photocatalysis, the applied bias can cause band bending and help the oriented transfer of the photogenerated electrons, decreasing the recombination of the photogenerated electron-hole pairs. The continuous photo-electrochemical reduction process in the filter-press cell is evaluated in terms of reaction rate (r), as well as Faradaic (FE) and energy (EE)
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