1. Proton OnSite, Wallingford, Connecticut 06492, USA;
2. Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA;
3. Department of Chemical and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut 06269, USA;
4. Forschungszentrum Jülich GmbH, 52425 Jülich, Germany;
5. National Renewable Energy Laboratory, Golden, Colorado 80401, USA;
6. Nel ASA, 0278 Oslo, Norway;