Abstract
Understanding the function of surface states on photoanodes is crucial for unraveling the underlying reaction mechanisms of water oxidation. For hematite photoanodes, only one type of surface states with higher oxidative energy (S1) has been proposed and verified as reaction intermediate, while the other surface state located at lower potentials (S2) was assigned to inactive or recombination sites. Through employing rate law analyses and systematical (photo)electrochemical characterizations, here we show that S2 is an active reaction intermediate for water oxidation as well. Furthermore, we demonstrate that the reaction kinetics and dynamic interactions of both S1 and S2 depend significantly on operational parameters, such as illumination intensity, nature of the electrolyte, and applied potential. These insights into the individual reaction kinetics and the interplay of both surface states are decisive for designing efficient photoanodes.
Highlights
Understanding the function of surface states on photoanodes is crucial for unraveling the underlying reaction mechanisms of water oxidation
We notice that a consistent assignment of iron-oxo species could be achieved for S1, while the possibility that S2 is a reaction intermediate cannot be absolutely excluded for two reasons: (i) we do observe a low but definitely positive steady-state photocurrent when S2 reaches its maximum density (Fig. 1d) and (ii) S2 is lower in energy, reaction kinetics need to be taken into consideration especially at higher external applied potentials
We here propose a dynamic interaction of both surface states, where their density and distribution depend on a wide range of experimental conditions In the following, we present detailed investigations of both surface states over a wide parameter range, using two complementary techniques
Summary
Understanding the function of surface states on photoanodes is crucial for unraveling the underlying reaction mechanisms of water oxidation. The reaction kinetics undergo a transformation to third-order (n = 3.36, kapp = 0.03 hole−2 nm[4] s−1, r2 = 0.99, Fig. 1f) when the hole density increases to a certain threshold value (~2.6 holes per nm−2).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
