Enhancing the Efficiency and Stability of NiO_x-Based Silicon Photoanode via Interfacial Engineering

Abstract

The photoelectrochemical performance of Si photoanode with a metal–insulator–semiconductor (MIS) structure is limited by weak Schottky barrier and poor charge transfer. In this work, a MIS structure, n-Si|dispersed NiSi x /NiO x patches|Au nanoparticles, is designed for efficient water oxidization with high stability. The photoanode exhibits a high activity with a low onset potential of ∼0.88 V and a high photocurrent density of ∼34 mA/cm2 at 1.23 V versus reversible hydrogen electrode (RHE), and retains excellent stability in 1.0 M NaOH for ∼10 h. We find that the improved photovoltage is contributed by the strengthened pinch-off effect of inhomogeneous Schottky barriers induced by the synergistic effect of decreased Schottky barrier height difference and increased depletion width in n-Si. We show that the enhanced photocurrent attributes to the reduced hole transport resistance by introducing high-conductive NiSi x and Au-NP bridge layers. Our findings demonstrate a promising strategy for the development of highly efficient and stable Si-based photoelectrodes for water oxidization.

Quantifying Losses and Assessing the Photovoltage Limits in Metal–Insulator–Semiconductor Water Splitting Systems

“…One design strategy to generate a large barrier height and photovoltage in MIS systems is to use high work function metals for n‐type systems (low work function metals for p‐type systems) 49,52,56. Another strategy to obtain a large barrier height is through the pinch‐off effect, where a high barrier electrolyte or oxide can compensate for low barrier electrocatalytic metal nanoparticles 29,32,34,40,41,57. Previous reports have also demonstrated that the insulator layer can serve as a passivation layer to remove defects and minimize barrier height losses from Fermi level pinning 50,51,53.…”

“…[49,52,56] Another strategy to obtain a large barrier height is through the pinch-off effect, where a high barrier electrolyte or oxide can compensate for low barrier electrocatalytic metal nanoparticles. [29,32,34,40,41,57] Previous reports have also demonstrated that the insulator layer can serve as a passivation layer to remove defects and minimize barrier height losses from Fermi level pinning. [50,51,53] Furthermore, several studies have shown that annealing is an effective method to further passivate interfacial defects and improve the photovoltage.…”

Atomically dispersed iridium catalysts on silicon photoanode for efficient photoelectrochemical water splitting

“…The free energy diagrams of OER at 0 V versus CHE are also provided in Supplementary Fig. 23. In addition, the reaction kinetics of Ir SAs/NiO (100) was examined to predict the kinetic barrier heights of the ratedetermining step via climbing image nudged elastic band (CI-NEB) calculations in Supplementary Fig.…”

“…Here, we report an atomic-scale-architectured Ir SAs/NiO/Ni/ ZrO 2 /n-Si photoanode device with drastically enhanced catalytic activity and stability. The NiO/Ni, which is highly catalytic and stable in alkaline condition, intrinsically has lots of Ni vacancies suitable for stabilization of single atoms [20][21][22][23][24] . As a result, it is possible to utilize the thin-film NiO/Ni as both a PEC catalyst and anchoring layer to capture metal atoms.…”

Junction Engineering in Si Photoanodes for Efficient Photoelectrochemical Water Splitting

“…Great effort has been focused on the integration of Si with a catalyst to improve the charge transfer kinetics and protect the semiconductor–electrolyte interface from corrosion. Coating the Si surface with transition metals, e.g., Co, Ni, Fe, and their composites or oxides has shown to efficaciously catalyze oxygen evolution reaction and protect Si from corrosion. − …”