Amorphous Cobalt Oxide Nanowalls as Catalyst and Protection Layers on n-Type Silicon for Efficient Photoelectrochemical Water Oxidation

Abstract

Silicon for photoelectrochemical (PEC) water splitting suffers from severe photocorrosion in the electrolyte and high overpotential at the interface with the electrolyte, although it is an earth-abundant material with a narrow band gap for the absorption of a wide range of the solar spectrum. Highly active transition-metal/metal oxides are considered promising materials for protecting the silicon surface, as they exhibit efficient catalytic properties which can reduce overpotential, thus improving the water splitting efficiency. In this study, electrodeposition, a simple and inexpensive method in comparison to vacuum processes such as atomic layer deposition and sputtering, was used to produce efficient Co-based catalysts on silicon substrates to fabricate photoanodes for the oxidation of water to generate oxygen. Distinctive morphologies of the Co-based catalysts were obtained by changing the types of additives in the precursor solution. The PEC performances of n-Si photoanodes with amorphous CoO x nanowalls (NWs) and Co nanoparticles (NPs) depended on the thicknesses and coverages of the catalysts. A fully covered CoO x NWs/n-Si photoanode exhibited stability higher than that of a partially covered Co NPs/n-Si photoanode. The optimized CoO x NWs/ n-Si photoanode exhibited an onset potential of 1.06 ± 0.01 V vs the reversible hydrogen electrode (RHE) and a photocurrent density of 23.3 ± 0.8 mA/cm 2 at 1.23 V vs RHE. A charge injection efficiency of almost 100% at 1.4 V vs RHE and high external quantum efficiency of 90% at 700 nm were achieved. These results show that morphology-controlled transition-metal-based catalysts fabricated by the facile electrodeposition method can be one of the promising pathways for the design of highperformance Si-based photoanodes.

Structural Properties of NdTiO2+xN1–x and Its Application as Photoanode

“…The CoO x decoration was supposed to accelerate the utilization of surface photogenerated holes to oxidize water, concurrently inducing extraction of deep charge carriers. 70 Thus, improvement PEC performance was achieved in Figure 7 .…”

Structural Properties of NdTiO2N and Its Application as Photoanode

“…The CoOx decoration was supposed to accelerate the utilization of surface photogenerated holes to oxidize water, concurrently inducing extraction of deep charge carriers. [64] Thus, improvement PEC performance was achieved in Fig. 7.…”

β-In2S3 as Water Splitting Photoanodes: Promise and Challenges

“…A PEC water splitting cell can be divided to a photocathode for hydrogen generation and a photoanode for oxygen generation. Since the oxygen evolution reaction (OER) includes four-electron-transfer process and the hydrogen evolution reaction (HER) requires two electrons, OER is the ratedetermining step in an overall water splitting, that is, the development of efficient photoanodes is important [78,79]. In a typical photoanode, when solar light is irradiated onto photoanodes, electron-hole pairs are produced in the semiconductor.…”