* Corresponding authors

^a Joint Center for Artificial Photosynthesis, California Institute of Technology, Pasadena, California 91125, USA
E-mail: gregoire@caltech.edu

^b Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA

^c Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA

^d Department of Materials Science and Engineering, University of California, Berkeley, CA 94720, USA

^e Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, USA

^f Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125, USA