Understanding and optimizing hematite photoelectrodes for photoelectrochemical water splitting.

摘要

The quest for carbon-neutral renewable energy to relax our reliance on the fossil fuels in the future has been the subject of extensive research. Among all the options, sunlight by far provides the most abundant and globally well-distributed source of energy. Capturing less than 1% of the sunlight energy illuminating the earth can entirely satisfy the world's energy demand. This work is thus focused on realizing hematite as an electrode material for solar water oxidation in a photoelectrochemical cell which produces clean burning, energy dense, hydrogen fuel. A combination of sunlight, water and earth abundant hematite, thus provides an essentially unlimited resource to produce solar hydrogen fuel.;Despite several attractive properties of hematite e.g. good light absorption, proper energy levels and stability, the experimental performances measured to date have fallen well short of the theoretical expectations. The poor performance has been generally attributed to recombination processes which limit charge separation and collection on this material. Consequently, a large input voltage is required to oxidize water on hematite, which is a major loss of efficiency. In this work hematite thin films papered by atomic layer deposition were systematically investigated under solar-driven water oxidation. A combination of electrochemical and photoelectrochemical, spectroscopic, and microscopic analysis were employed to better understand the fundamental mechanisms behind the poor performance. Performance enchantment strategies were then developed and successfully employed to boost the water oxidation performance of the electrodes. For example, substrate modification was shown that enables the deposition of highly crystalline hematite which reduces bulk recombination. The surface recombination on the other hand, was eliminated by a combination of high temperature annealing and addition of catalysts. Finally a simple and universal electrodeposition method was established to deposit highly active hematite photoelectrodes, providing a promising route to achieve efficient water splitting using this material.