Graphene as a protective layer for silicon in an aqueous PEC cell

Graphene may be an almost ideal protection layer for semiconductor photoelectrodes. It can be grown in nearly pinhole-free large area layers and has been shown to inhibit the oxidn. of metals in air as well as in aq. electrochem. environments. In this study, the chem., electrochem., and photoelectrochem. behavior of graphene-coated n-type Si(111) photoanodes was compared to that of H-terminated and Me terminated n-type Si(111) photoanodes in contact with aq. K_3[Fe(CN)_6]/K_4[Fe(CN)_6] as well as in contact with a series of oneelectron redox couples in non-aq. electrolytes. The n-Si/Graphene electrodes exhibited stable short-circuit photocurrent densities of over 10 mA cm^(-2) for over 1000 s of operation in aq. electrolyte, whereas n-Si-H and n- Si-Me electrodes yielded nearly complete decay of the c.d. within approx. 30 s and 120 s, resp. The values of the open-circuit photovoltages and the flat-band potentials of the Si were a function of both the Fermi level of the graphene and the electrochem. potential of the electrolyte soln., indicating that the n-Si/Graphene interface did not form a buried junction with the soln. contact. The use of addnl. layers of graphene further improved stability while leading to a junction that was increasingly pinned by the Si/graphene interface. Finally, the chem. stability of graphene in acidic and basic environments relevant to solar water splitting was demonstrated and the possibility for non-covalent hydrogen evolution catalyst attachment via pi-pi interactions between graphene and pyrene moieties appended to known mol. hydrogen evolution catalysts was explored