Retraction of: Nature Communications https://doi.org/10.1038/ncomms6883, published online 19 December 2014.

During follow-up work to this Article, the authors discovered that its main claim—namely, that CO2 was reduced to form oxalate—is incorrect. Rather, the detected oxalate is formed by the oxidation of ascorbate in the system, as discussed in a subsequent analysis1. Although other results reported therein are valid, the authors wish to retract this Article.