Reduced Graphene Oxide as a Catalyst Binder: Greatly Enhanced Photoelectrochemical Stability of Cu(In,Ga)Se₂ Photocathode for Solar Water Splitting

Abstract

The photoelectrochemical (PEC) properties of a Cu(In,Ga)Se2 (CIGS) photocathode covered with reduced graphene oxide (rGO) as a catalyst binder for solar‐driven hydrogen evolution are reported. Chemically reduced rGO with various concentrations is deposited as an adhesive interlayer between CIGS/CdS and Pt. PEC characteristics of the CIGS/CdS/rGO/Pt are improved compared to the photocathode without rGO due to enhancement of charge transfer via efficient lateral distribution of photogenerated electrons by conductive rGO to the Pt. More importantly, the introduction of rGO to the CIGS photocathode significantly enhances the PEC stability; in the absence of rGO, a rapid loss of PEC stability is observed in 2.5 h, while the optimal rGO increases the PEC stability of the CIGS photocathode for more than 7 h. Chemical and structural characterizations show that the loss of the Pt catalyst is one of the main reasons for the lack of long‐term PEC stability; the introduction of rGO, which acts as a binder to the Pt catalysts by providing anchoring sites in the rGO, results in complete conservation of the Pt and hence much enhanced stability. Multiple functionality of rGO as an adhesive interlayer, an efficient charge transport layer, a diffusion barrier, and protection layer is demonstrated.

Fullerene as a Photoelectron Transfer Promoter Enabling Stable TiO2‐Protected Sb2Se3 Photocathodes for Photo‐Electrochemical Water Splitting

“…Although solution‐based carbon‐precursor coating followed by high‐temperature annealing (550 °C, N 2 atmosphere) has been carried out to create a uniform protective carbon layer surrounding a Cu 2 O nanowire photocathode (improving its stability as well as photocurrent density), this complex multistep coating procedure was inadequate as a versatile tool for various p‐type semiconductor materials . Recently, Koo et al demonstrated the use of reduced graphene oxide as a catalyst binder onto a CdS/CuInGaSe 2 photocathode, exhibiting multifunctional advantages including not only the physical binding of the Pt catalyst, but also preventing the in‐diffusion of Pt and the corrosion of the CdS layer . Despite the significantly enhanced long‐term stability achieved (no degradation up to 7 h under a pH of 6.8), detailed understanding of the degradation mechanism as well as the behavior of the photogenerated electrons was still elusive.…”

“…[6,7] In this respect, an interface modification to promote photoelectron transfer from TiO 2 to a cocatalyst would lead to improving the PEC stability of the TiO 2 -protected photocathode by hampering TiO 2 photoreduction. [29] Despite the significantly enhanced longterm stability achieved (no degradation up to 7 h under a pH of 6.8), detailed understanding of the degradation mechanism as well as the behavior of the photogenerated electrons was still elusive. Although solutionbased carbon-precursor coating followed by high-temperature annealing (550 °C, N 2 atmosphere) has been carried out to create a uniform protective carbon layer surrounding a Cu 2 O nanowire photocathode (improving its stability as well as photo current density), this complex multistep coating procedure was inadequate as a versatile tool for various p-type semiconductor materials.…”

Si/CuIn0.7Ga0.3Se2 Core–Shell Heterojunction for Sensitive and Self‐Driven UV–vis–NIR Broadband Photodetector

“…CuIn x Ga 1− x Se 2 (CIGS) in its chalcopyrite phase has attracted considerable interest as a promising p‐type light absorber, owing to its tunable band energy (1.0–1.7 eV), large optical absorption coefficient (≈10 5 cm −1 ), outstanding thermal, environmental and electrical stabilities . In terms of application, CIGS thin films have been used in thin‐film solar cells, solar modules, and photoelectrochemical photocathodes . The above‐stated excellent features also make CIGS great potential application in broadband photodetection.…”

Graphitic carbon nitride (g‐C3N4)‐based nanosized heteroarrays: Promising materials for photoelectrochemical water splitting

“…All photoelectrodes discussed above are photoanodes based on n‐type semiconductors, which are commonly used to perform OER. In contrast, the p‐type semiconductor material can also be utilized as photocathodes to perform HER under the incident light radiation 169‐171 …”