Nature Chemistry 5, 1035–1041 (2013); Published online 20 October 2013; corrected after print 22 April 2014.

In the version of this Article previously published, some incorrect data were included in Fig. 1e. The initial data were inadvertently repeated as the data for 20,000 cycles, and the total number of cycles was stated as 50,000 when it should have been 43,000. An error corresponding to the latter was also made in the first full sentence on page 1037. Figure 1e should have appeared as shown below. These errors have been corrected in the online versions of the Article.