1. School of Electrical and Electronic Engineering Nanyang Technological University 50 Nanyang Avenue Singapore 639798 Singapore
2. Institute of Sustainability for Chemical Energy and Environment (ISCE2) Agency of Science Technology and Research (A*STAR) 1 Pesek Road Singapore 627833 Singapore
3. Institute of Materials Research and Engineering (IMRE) Agency of Science Technology and Research (A*STAR) 2 Fusionopolis Way, Innovis Singapore 138634 Singapore
4. Department of Chemistry University of Oxford Oxford OX1 3TA UK
5. Department of Chemistry National University of Singapore 3 Science Drive 3 Singapore 117543 Singapore
6. Andlinger Center for Energy and the Environment, and Department of Electrical and Computer Engineering Princeton University Princeton 08544 USA