Photoelectrochemical Properties of GaN Photoanodes with Cobalt Phosphate Catalyst for Solar Water Splitting in Neutral Electrolyte

Abstract

Cyclic voltammetry measurements are carried out in neutral phosphate-buffered electrolyte using n-type Gapolar GaN thin-film photoelectrodes with and without cobalt phosphate (Co-Pi) modification. Without Co-Pi, the variation of the photocurrent with the bias potential exhibits a two-step behavior and under chopped illumination spikes occur at low bias potential. Thus in this regime surface recombination is dominant. Co-Pi modification suppresses surface recombination and significantly increases the photocurrent, especially for low bias potentials. At the same time, stability tests reveal that Co-Pi does not protect GaN against photocorrosion. Experiments using H 2 O 2 imply that this photocorrosion is a reductive process and probably related to the presence of charged surface defects.

Triple Planar Heterojunction of SnO2/WO3/BiVO4 with Enhanced Photoelectrochemical Performance under Front Illumination

“…Usually, spikes in the transient photocurrent measurements indicate surface recombination, due to the presence of the surface states or slow water oxidation kinetics. SnO 2 /WO 3 /BiVO 4 photoanode shows negligible spikes and a steady photocurrent, which demonstrates that the holes accumulated at the surface readily react with the water and hence improve photocurrent density without producing transient spikes [31].…”

“…It indicates that the SnO 2 50 nm/WO 3 50 nm/BiVO 4 has high charge separation efficiency and high water oxidation kinetics. photocurrent, which demonstrates that the holes accumulated at the surface readily react with the water and hence improve photocurrent density without producing transient spikes [31]. Further, charge transfer properties have been investigated by Nyquist plots.…”

Rational Design and Construction of Cocatalysts for Semiconductor‐Based Photo‐Electrochemical Oxygen Evolution: A Comprehensive Review

“…It is reported that Co-Pi can change the reaction pathway to reduce overpotential and promote surface charge transfer kinetics. [96,109] For example, Carroll and Gamelin [96] reported that water-oxidation kinetics of α-Fe 2 O 3 actually gets slow after the deposition of Co-Pi, but electron-hole recombination slows even more, resulting in a net enhancement of water-oxidation quantum efficiency, which is opposite to previous expectations. Meanwhile, as the change in valence state of Co ion is invertible, the accumulation of photoinduced holes at the interface of electrode and electrolyte can be relieved timely and effectively and then an improved PEC performance can be achieved.…”

“…Since then, this catalyst has gained numerous interests and become one of the research hotspots. [96,102,[108][109][110][111][112] Some further clarified the mechanism of the Co-Pi applied on semiconductors. [107] Co 2+/3+ of Co-Pi can be oxidized to a higher valence state of Co 4+ under the effect of current or holes, and then Co 4+ can be reverted back to Co 2+/3+ rapidly after it oxidized water molecules or sacrificial agents, [50] which is recognized as an entire catalytic reaction cycle.…”

InGaN/GaN Multiple Quantum Well Photoanode Modified with Cobalt Oxide for Water Oxidation

“…Moreover, Co-Pi-modified GaN photoaonde has shown some improvement in the onset potential and the photocurrent but poor resistance against photocorrosion 16 .…”