Efficient Photoelectrochemical Hydrogen Evolution Using Pseudocapacitive NiO<sub><i>x</i></sub>/Si Junction with Misaligned Energy Levels

Published on 2019-01-11T19:51:55Z (GMT) by
Photoelectrochemical (PEC) water splitting performed by an electrocatalyst integrated with a semiconducting photoelectrode is advantageous with improvements in both charge-transfer kinetics and interface energetics because of the electrocatalyst/semiconductor junction. In general, interface energetics has been considered to arise from differences in the intrinsic electronic energy levels between the electrocatalyst and the semiconductor. Here, we demonstrated that when a NiO<sub><i>x</i></sub> thin film with porous and nanocrystalline structures is integrated with a Si photoelectrode, the interface energetics is developed by an electrochemical energy level extrinsically formed by the pseudocapacitive surface reaction (a redox reaction of NiO<sub><i>x</i></sub> for electrochemical charge storage). This new type of junction, named a pseudocapacitive NiO<sub><i>x</i></sub>/Si junction, revealed two intriguing features: the interface energetics is dynamically changed as charging/discharging progresses, and the developed electrochemical energy level and the electronic energy level of Si are abnormally misaligned under equivalent circuit conditions. With these features, the open circuit potential (<i>V</i><sub>oc</sub>) of the PEC device was determined by the degree of misalignment (i.e., the electrochemical energy level). The electrochemical energy level was maximized by ∼1 V through the insertion of a SiO<sub>2</sub> interfacial layer thick enough to suppress discharge and 1 h of PEC operation for sufficient charging by the transfer of light-induced electrons. As a result, the highest <i>V</i><sub>oc</sub> of ∼1 V, surpassing the theoretical limit of 0.85 V in Si photovoltaics, was achieved. This finding demonstrated a new paradigm for self-powered PEC reactions.

Cite this collection

Jung, Jin-Young; Yu, Jin-Young; Wehrspohn, Ralf B.; Lee, Jung-Ho (2019): Efficient Photoelectrochemical Hydrogen Evolution

Using Pseudocapacitive NiOx/Si Junction

with Misaligned Energy Levels. ACS Publications. Collection.