The Potential of Photoelectrochemical Carbon Sinks

Abstract

Greenhouse gas emissions must be cut to limit global warming to 1.5-2 • C above preindustrial levels. Yet the rate of decarbonisation is currently too low to achieve this. Policy-relevant scenarios therefore rely on the permanent removal of CO 2 from the atmosphere. However, none of the envisaged technologies has demonstrated scalability to the decarbonization targets for the year 2050. In this analysis, we show that artificial photosynthesis for CO 2 reduction may deliver an efficient large-scale carbon sink. This technology is mainly developed towards solar fuels and its potential for negative emissions has been largely overlooked. With high efficiency and low sensitivity to high temperature and illumination conditions, it could, if developed towards a mature technology, present a viable approach to fill the gap in the negative emissions budget. Broader contextThe current CO 2 emission rate and its near-future development is expected to be incompatible with the worldwide carbon budget associated with a 2 • C target for global warming. Negative emission technologies are therefore becoming an increasingly important basis for climate policy scenarios, but while their scalability is necessary, it is not yet given. Biomass-based approaches for typical negative-emission targets require a significant fraction of the worldwide available arable land. We show that photoelectrochemical CO 2 reduction might be a viable alternative, that also offers a greatly reduced competition with food production. To develop this approach further, reaction paths should be optimised for carbon removal efficiency, and not for their energetic efficiency as in solar fuel applications.