Thorne James E, Jang Ji-Wook, Liu Erik Y, Wang Dunwei
Department of Chemistry , Boston College , Merkert Chemistry Center , 2609 Beacon St. , Chestnut Hill , MA 02467 , USA . Email:
Chem Sci. 2016 May 1;7(5):3347-3354. doi: 10.1039/c5sc04519c. Epub 2016 Feb 11.
Photoelectrochemical (PEC) water splitting holds the potential to meet the challenges associated with the intermittent nature of sunlight. Catalysts have often been shown to improve the performance of PEC water splitting, but their working mechanisms are not well understood. Using intensity modulated photocurrent spectroscopy (IMPS), we determined the rate constants of water oxidation and recombination at the surface of three different hematite-based photoanodes. It was found that the best performing electrodes, in terms of photocurrent onset potential, exhibited the slowest water oxidation rate constants, which was a surprise. The performance of these photoelectrodes was enabled by the slow surface recombination. When amorphous NiFeO , a water oxidation catalyst, was present, the rate of surface hole transfer actually slowed down; what was slowed more was the recombination rate at the hematite surface, resulting in better water oxidation performance. As such, NiFeO primarily serves as a passivation layer rather than a catalytic layer. Together a better understanding of the role of catalytic overlayers for water oxidation has been achieved.
光电化学（PEC）水分解有潜力应对与阳光间歇性相关的挑战。催化剂常常能提高PEC水分解的性能，但其作用机制尚未得到很好的理解。利用强度调制光电流光谱（IMPS），我们测定了三种不同的赤铁矿基光阳极表面水氧化和复合的速率常数。结果发现，就光电流起始电位而言，性能最佳的电极表现出最慢的水氧化速率常数，这令人惊讶。这些光电极的性能得益于缓慢的表面复合。当存在水氧化催化剂非晶态NiFeO时，表面空穴转移速率实际上减慢了；更慢的是赤铁矿表面的复合速率，从而带来了更好的水氧化性能。因此，NiFeO主要起到钝化层而非催化层的作用。由此，我们对催化覆盖层在水氧化中的作用有了更好的理解。
