Addendum to: Nature Catalysis, published online 17 December 2018.

Nature Catalysis is publishing an editorial expression of concern on this article because of a repeating noise pattern in the chronoamperometry plot of Fig. 4f. The authors have informed us that the raw data for this plot is unavailable. The authors have provided new experimental data to support the findings and we are currently investigating the issue further, in consultation with independent experts. We will provide an update once a conclusion is reached. All authors agree with the publication of this note.