Abstract
AbstractThe 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 NiO and NiNi (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.
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