Efficient photoelectrochemical water oxidation enabled by an amorphous metal oxide-catalyzed graphene/silicon heterojunction photoanode

Silicon is a promising photoelectrochemical (PEC) material owing to its earth abundance, high carrier mobility and narrow bandgap. However, a bare Si photoelectrode is prone to photocorrosion and its photovoltage is affected by surface states on the electrode in PEC measurements. In the present work, a simple and inexpensive method for the construction of a Si/graphene heterojunction is presented. The high barrier at the solid/solid junction results in an open-circuit voltage of 490mV, making it an excellent heterojunction light absorber to generate a substantial photovoltage for PEC water oxidation. A TiO2 thin layer deposited on the Si/graphene structure is effective to protect the heterojunction from the electrolyte while favoring the interfacial charge transport from the buried junction. The introduction of a FeNiCoOx co-catalyst thin film onto the TiO2 protected heterojunction yields a high photocurrent density of approximate to 19 mA cm(-2) at an applied potential of 1.5 V vs. RHE in 1.0 M NaOH solution under one sun simulated solar illumination. In contrast to the unprotected Si/graphene electrode, the activity of the TiO2 protected photoanode is sustained for several hours in an alkaline electrolyte. This work clearly reveals the important role of graphene in the performance improvement of the Si-based photoanodes and sheds light on the introduction of novel materials onto silicon-based electrodes to achieve higher photovoltages for efficient PEC reactions.