Solar conversion of CO2 to CO using Earth-abundant electrocatalysts prepared by atomic layer modification of CuO

Abstract

The solar-driven electrochemical reduction of CO 2 to fuels and chemicals provides a promising way for closing the anthropogenic carbon cycle. However, the lack of selective and Earth-abundant catalysts able to achieve the desired transformation reactions in an aqueous matrix presents a substantial impediment as of today. Here we introduce atomic layer deposition of SnO 2 on CuO nanowires as a means for changing the wide product distribution of CuO-derived CO 2 reduction electrocatalysts to yield predominantly CO. The activity of this catalyst towards oxygen evolution enables us to use it both as the cathode and anode for complete CO 2 electrolysis. In the resulting device, the electrodes are separated by a bipolar membrane, allowing each half-reaction to run in its optimal electrolyte environment. Using a GaInP/GaInAs/Ge photovoltaic we achieve the solar-driven splitting of CO 2 into CO and oxygen with a bifunctional, sustainable and all Earth-abundant system at an e ciency of 13.4%.T he electrochemical reduction of CO 2 to fuels and chemicals has the promise to provide a versatile way of storing renewable electrical energy in chemical bonds while simultaneously closing the anthropogenic carbon cycle. A number of products have been successfully synthesized by this process, most notably carbon monoxide (CO) 1-3 , formic acid (HCOOH), methane (CH 4 ) 4 , ethylene (C 2 H 4 ) 5 and ethanol (CH 3 CH 2 OH) 6 , as well as other compounds 7,8 . Due to the numerous possible reaction pathways, selectively targeting one specific product at high yield has remained a challenge, which, to the present day, has been achieved only for CO and formic acid in aqueous electrolytes. Unfortunately, selective electroreduction of CO 2 to these products relies on the use of precious metals (Au, Ag, Pd) [9][10][11][12] , requires operation at considerable overpotentials 13 , or requires the use of electrolyte additives, such as ionic liquids 14 . Developing inexpensive, selective and stable catalysts operating at low overpotentials is therefore a crucial requirement.Recently, substantial progress toward decreasing the overpotential of copper-based electrodes was made by employing catalysts derived from copper oxides 15 . However, the insufficient selectivity remained an issue, with the catalyst producing CO, H 2 and formic acid at comparable selectivities. Following up on this work, it was demonstrated that by electrochemically reducing copper oxide in the presence of indium ions, the selectivity toward producing CO could be substantially enhanced 16,17 . More recently, the same group demonstrated tin to have a similar effect 18 . Although adding sources of metal ions during the catalyst reduction process is effective in tuning the selectivity, it is difficult to control and may not guarantee uniform coating.Here, we demonstrate the surface modification of CuO nanowire electrodes with SnO 2 using atomic layer deposition (ALD), leading to a highly selective catalyst for the electrochemical reduction of CO 2 to CO. By using SnO 2 -modified...

The Potential of Photoelectrochemical Carbon Sinks

“…The greatest challenges to overcome towards the application are, for now, to develop and implement systems that are stable under operating conditions, as well as the derivation of earth-abundant, efficient catalysts. [14][15][16]27 …”

“…Artificial photosynthesis already delivers fivefold higher efficiencies, as 13% for CO 2 reduction and 16-19% for solar water splitting have recently been demonstrated. [14][15][16] Using solar fuels, either hydrogen or carbon-based from CO 2 reduction, would cut greenhouse gas emissions. However, while the combustion product of solar hydrogen is water, using renewably generated carbon-based fuels releases the captured greenhouse gas back into the atmosphere.…”

Recent progress on advanced design for photoelectrochemical reduction of CO2 to fuels

“…To suppress the hydrogen evolution and overcome the limitation of noble metal catalyst, they chose earth-abundant catalyst (i.e., CuO nanowires with SnO 2 surface modification by atomic layer deposition) as both anode and cathode (Fig. 18a) [48]. The SnO 2 layer on surface could largely enhance the selectivity of CO production.…”

“…Recently, a novel tandem device coupling a photovoltaic cell for photoelectrical conversion with an efficient electrocatalyst for catalysis has been developed for CO 2 reduction (Fig. 1d), also demonstrating the excellent efficiency and promising potential [47,48].…”

Conditions for capture

“…Using solardriven catalytic reactions to generate useful precursors such as CO, which can be used for synthesis of a range of products, might be especially attractive. Indeed, efforts to increase the activity and product selectivity of Earth-abundant catalysts 7 and to engineer solar-to-chemical systems with the potential for scalability 8 are key to improving the feasibility of such processes.…”