Type II Heterostructures: The Way Towards Improved Photoelectrochemical Activity of Graphitic Carbon Nitride
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Photoelectrochemical (PEC) water splitting is promising approach of solar energy conversion. Graphitic carbon nitride can be given as an example of metal-free and cheap semiconducting material for photoelectrochemical reactions however its activity is very low, probably due to high rate of unfavorable charge carriers recombination. Type II heterostructure, graphitic carbon nitride–copper oxide (g-C3N4 and CuO), showed improved photoelectrochemical activity in comparison with neat g-C3N4. Visible-light irradiated composite generates cathodic photocurrents under middle bias and therefore it can be used as a photocathode for water splitting with hydrogen formation. The band bending existing in type II heterostructures drives the photogenerated electrons and holes to move in opposite directions, resulting in a spatial separation of the photogenerated charge carriers on different sides of heterojunction. Lower recombination rate and higher activity are the overall effects. Moreover, by using copper based underlayer (metallic copper) or overlayer (copper iodide) the PEC activity grows. In particular CuI@g-C3N4_CuO showed the highest photocurrent density and the “relax time” in dark conditions has an noticeable influence on the further increase in activity.
Keywordsg-C3N4 Inorganic composites Photocathode PEC water splitting Copper oxides
This research was supported by National Science Centre, Poland—Project SONATA 2016/21/D/ST4/00221.