Charge Transfer Kinetics of Photo-Electrochemical Hydrogen Evolution Improved by Nonstoichiometric N

Advanced Sustainable Systems 2(2) 1700138

https://doi.org/10.1002/adsu.201700138

Jin-Young Jung, Jin-Young Yu, Sanghwa Yoon, Bongyoung Yoo, Jung-Ho Lee

Abstract

The integration of electrocatalyst (EC) with light-absorbing semiconductor photoelectrode is regarded as a representative framework for photoelectrochemical (PEC) devices. When considering the charge transfer pathways, PEC performance is governed by the charge kinetics at the EC/electrolyte and the semiconductor/EC interfaces. Here, systematic investigations are reported, made on the overall kinetics of the PEC hydrogen evolution reaction (HER) in an alkaline electrolyte. A non-stoichiometric (Ni-rich) NiOx (x < 1) EC is deposited on a Si photocathode passivated with a SiOx layer. A few distinctive features of the Ni-rich NiOx film are identified in contrast with the conventional O-rich NiOy (y ≥ 1) which could lower the series resistance along the charge transfer pathways. The Ni-rich NiOx is found to possess both NiO and NiNi (by oxygen-vacancy) bonds, which act as suitable catalytic sites for dissociating water molecules and recombining two hydrogen atoms, respectively. In addition, the Ni-rich NiOx reveals both n-type and metallic conduction behavior, a feature that may contribute to lowering bulk resistance as well as tunneling resistance through SiOx layer. As a result, this noble metal-free EC-integrated Si photocathode achieves the highest potential of 0.41 V vs. reversible hydrogen electrode to produce a photocurrent density of 10 mA cm2.