A prototype reactor for highly selective solar-driven CO₂reduction to synthesis gas using nanosized earth-abundant catalysts and silicon photovoltaics

Abstract

The conversion of carbon dioxide (CO2) into value-added chemicals and fuels, preferably using renewable energy and earth-abundant materials, is considered a key priority for future energy research. In this work, a bias-free reactor device for the solar-driven conversion of CO2 to synthesis gas (syngas) has been developed. The integrated fluidic device consists of a cathode made of copper foam coated with low-cost nanosized zinc flakes as catalyst to perform the CO2 reduction reaction (CO2RR) to syngas, an adapted silicon heterojunction solar cell structure as photoanode with nickel foam as catalyst to facilitate the oxygen evolution reaction (OER), and a bipolar membrane separating the respective catholyte and anolyte compartments. The membrane allows for the operation of the catholyte and anolyte at different pH values. Stable and tunable hydrogen-to-carbon monoxide (H2:CO) ratios between 5 and 0.5 along with high CO Faradaic efficiencies of up to 85% and CO current densities of 39.4 mA cm-2 have been demonstrated. Under photoelectrolysis conditions, the photovoltage of the photoanode was varied between 0.6 V and 2.4 V by connecting up to four heterojunction solar cells in series, and thus reducing the overall cell voltage solely by solar energy utilization. Bias-free operation of the integrated device has been achieved under ambient conditions with active areas for CO2RR and OER, respectively, of 10 cm2. An operation current density of 5.0 mA cm-2 was measured under 100 mW cm-2 illumination of the complete device, which corresponds to a solar-to-syngas conversion efficiency of 4.3%.Postprint (author's final draft

Zn–Cu Alloy Nanofoams as Efficient Catalysts for the Reduction of CO2 to Syngas Mixtures with a Potential‐Independent H2/CO Ratio

“…Previous reports have focused on monometallic molecular and heterogeneous catalytic systems, which have been used for simultaneous production of CO and H 2 . However, single catalytic sites offer limited possibilities for selective tuning of the catalyst.…”

“…Previous reports have focusedo nm onometallic molecular [4][5][6] and heterogeneousc atalytic systems, [7][8][9][10][11][12][13][14][15] which have been used fors imultaneous production of CO and H 2 .H owever,s ingle catalytic sites offer limited possibilities for selective tuning of the catalyst. Introducing as econd metal site offers an extra degree of freedom in catalystd esign ando ffers the best route to address the above criteria.…”

Sharp‐Tipped Zinc Nanowires as an Efficient Electrocatalyst for Carbon Dioxide Reduction

“…Researchers have revealed the high‐activity of noble‐metal electrodes (e.g., gold and silver) for CO 2 ‐to‐CO reduction, but the high cost limits the industrial applications. Zinc (Zn) is an earth‐abundant metal and recent studies have demonstrated the capacity of Zn as an efficient electrocatalyst for CO 2 reduction to primarily CO . Won et al.…”

“…[10] Researchers have revealed the high-activity of noblemetal electrodes (e.g.,g old and silver) for CO 2 -to-CO reduction, [11][12][13] but the high cost limits the industrial applications. Zinc (Zn) is an earth-abundantm etal and recent studies have demonstrated the capacity of Zn as an efficient electrocatalyst for CO 2 reduction to primarily CO. [14][15][16][17][18][19] Wone tal. have shown exciting results on ah ierarchical hexagonal Zn catalyst with the maximum selectivityo fa bout9 5% for CO, [14] indicating the decisive role of morphology of different Zn catalysts.…”

Multilayered Hematite Nanowires with Thin‐Film Silicon Photovoltaics in an All‐Earth‐Abundant Hybrid Tandem Device for Solar Water Splitting

“…The 3 D structure of the applied Ni foam offered a higher active surface area compared with the flat foil, which should be conducive to better HER catalysis of the photocathode. This has been shown elsewhere, and was confirmed herein by the j–V measurement presented in Figure S8 (Supporting Information), proving a shift of the onset potential for the cathodic current density in the anodic direction as well as the steeper slope in the j – V characteristics of the Ni foam compared with a Ni foil electrode. These results were reflected in the linear sweep curves shown in Figure , as the fill factor of the photocathode (filtered) increased significantly, indicating enhanced kinetics of the HER.…”