Nanoengineered Advanced Materials for Enabling Hydrogen Economy: Functionalized Graphene–Incorporated Cupric Oxide Catalyst for Efficient Solar Hydrogen Production

Abstract

Cupric oxide (CuO) is a promising candidate as a photocathode for visible‐light‐driven photo‐electrochemical (PEC) water splitting. However, the stability of the CuO photocathode against photo‐corrosion is crucial for developing CuO‐based PEC cells. This study demonstrates a stable and efficient photocathode through the introduction of graphene into CuO film (CuO:G). The CuO:G composite electrodes are prepared using graphene‐incorporated CuO sol–gel solution via spin‐coating techniques. The graphene is modified with two different types of functional groups, such as amine (NH2) and carboxylic acid (COOH). The COOH‐functionalized graphene incorporation into CuO photocathode exhibits better stability and also improves the photocurrent generation compare to control CuO electrode. In addition, COOH‐functionalized graphene reduces the conversion of CuO phase into cuprous oxide (Cu2O) during photo‐electrochemical reaction due to effective charge transfer and leads to a more stable photocathode. The reduction of CuO to Cu2O phase is significantly lesser in CuO:G‐COOH as compared to CuO and CuO:G‐NH2 photocathodes. The photocatalytic degradation of methylene blue (MB) by CuO, CuO:G‐NH2 and CuO:G‐COOH is also investigated. By integrating CuO:G‐COOH photocathode with a sol–gel‐deposited TiO2 protecting layer and Au–Pd nanostructure, stable and efficient photocathode are developed for solar hydrogen generation.

Photoelectrochemical Water‐Splitting Using CuO‐Based Electrodes for Hydrogen Production: A Review

“…In contrast, pure CuO electrode degraded rapidly and only retained 20% of its initial current after 600 s. One reason for the photocurrent reduction in the CuO‐based composites might be the instability of this material under irradiation since CuO converts to Cu 2 O and metallic Cu over time. [ 277 ] This phenomenon can be explained by using XPS analysis before and after the PEC test. As can be seen in Figure 7e–g, after PEC measurements, tiny shoulder peaks at 932.3 and 952.3 eV appeared for CuO and CuO:G‐NH 2 films in XPS spectra, indicating the photo‐corrosion phenomenon at these electrodes.…”

“…As can be seen in Figure 7e–g, after PEC measurements, tiny shoulder peaks at 932.3 and 952.3 eV appeared for CuO and CuO:G‐NH 2 films in XPS spectra, indicating the photo‐corrosion phenomenon at these electrodes. [ 277 ] One of the reasons that inhibits the photo‐corrosion of CuO in the CuO:G‐COOH electrode is the electron acceptance property of the –COOH in graphene, which can capture the electron easily to prevent CuO from accessing free electrons as a result of its reduction. Another reason is that –NH 2 has electron donor property in the CuO:G‐NH 2 electrode, in which the reduction of CuO into Cu 2 O occurs when it supplies free electrons.…”

“…Another reason is that –NH 2 has electron donor property in the CuO:G‐NH 2 electrode, in which the reduction of CuO into Cu 2 O occurs when it supplies free electrons. [ 277 ] Figure 7h,i show the photo‐corrosion of CuO electrode (conversion of CuO to Cu 2 O) before and after PEC measurement. The areas related to Cu 2 O in the morphology of the CuO electrode before and after the water splitting under the light illumination were much smaller than other electrodes under similar conditions, confirming previous results.…”

“…Based on the results of PEC characteristics (see Figure 7c,d), it was found that the CuO:G‐COOH photoelectrode with a 0.04 g of graphene content with a current density of 1.32 mA cm −2 at 0 V versus RHE has the best performance among all the synthesized photoelectrodes. [ 277 ] Wu et al. [ 254 ] synthesized Cu 2 O/CuO/rGO nanosheets by a facile one‐pot hydrothermal process.…”

“…[ 269 ] In another study, Dalapati et al. [ 277 ] deposited the CuO films in the presence of poly(ethylene glycol) using the spin‐coating technique and then incorporated graphene into the CuO. The results showed that the formation of heterojunction between these two materials led to enhanced electrode stability and photoelectric properties.…”