Electrochemical and Photoelectrochemical Transformations of Aqueous CO2
This chapter covers the electrochemical and photoelectrochemical conversion of CO2 in aqueous media. It is divided into sections that consider heterogeneous electrocatalysts on metal electrodes, homogeneous catalysts interacting with metal surfaces, light
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Electrochemical and Photoelectrochemical Transformations of Aqueous CO2 Aubrey R. Paris, Jessica J. Frick, Danrui Ni, Michael R. Smith and Andrew B. Bocarsly
Abstract
This chapter covers the electrochemical and photoelectrochemical conversion of CO2 in aqueous media. It is divided into sections that consider heterogeneous electrocatalysts on metal electrodes, homogeneous catalysts interacting with metal surfaces, light-driven semiconductor electrodes, and hybrid systems that combine heterogeneous interfaces with surface-confined molecular components.
7.1
Introduction
It has been suggested that CO2 may be a “drop in” chemical feedstock replacement for petroleum and natural gas. To fulfill that role, it must be possible to produce both fuels and bulk organic starting materials from CO2. One major challenge to adopting this vision is that CO2 represents a highly oxidized form of carbon, whereas fossil fuels are primarily composed of highly reduced carbon compounds. Thus, converting CO2 into a “replacement fossil resource” involves the development of a rich and cost-effective reduction chemistry. Cathodic electrochemical processes provide a viable route to achieving that goal. To avoid further consumption of fossil fuels and the generation of the undesirable greenhouse gas CO2, the transformations of interest must be driven by an alternate energy source. While any alternative energy resource that allows for efficient production of electricity is viable in this regard, solar energy-derived electricity provides a very appealing mimic of the geobiological processes that gave rise to our fossil fuel reserves. To that end, two different electrochemical configA. R. Paris J. J. Frick D. Ni M. R. Smith A. B. Bocarsly (&) Department of Chemistry, Princeton University, Princeton, NJ 08544, USA e-mail: [email protected] © Springer Nature Switzerland AG 2019 M. Aresta et al. (eds.), An Economy Based on Carbon Dioxide and Water, https://doi.org/10.1007/978-3-030-15868-2_7
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urations are conceivable: (1) a classic metal electrode-based electrochemical cell coupled to a photovoltaic panel or (2) a photoelectrochemical cell consisting of one or two semiconductor electrodes directly immersed in an electrolyte as shown in Fig. 7.1. Both systems can be said to perform artificial photosynthesis, although that term has traditionally been applied to systems that specifically split H2O to generate H2 and O2. More recently the term solar fuels has been used to describe light-driven electrochemistry, be it water splitting or CO2 reduction. However, this term ignores the fact that a major motivation for electrochemically reducing CO2 is the formation of feedstocks for organic synthesis. Thus, a more creative term that
Fig. 7.1 The two possible light-driven electrochemical devices for the conversion of CO2 to organic products. a A photovoltaic system coupled to an electrochemical cell composed of two half cells employing metallic electrodes. This system requires coupling electronics (z-matching) to alig
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