On April 24th, Beijing time, the top international academic journal "Nature" published online the joint research progress in the field of photoelectrochemical hydrogen production by Professor Luo Jingshan's research group from the School of Electronic Information and Optical Engineering at Nankai University, in collaboration with teams from the University of Cambridge in the UK and the Swiss Federal Institute of Technology in Lausanne.
The research team prepared three different-oriented single-crystal cuprous oxide (Cu2O) thin films using solution-phase epitaxial growth technology. They quantitatively analyzed the anisotropic photoelectrochemical properties of Cu2O using femtosecond transient reflectance spectroscopy. Based on the analysis conclusions, they developed and prepared polycrystalline Cu2O photoelectrodes with [111] as the main crystal orientation, achieving a breakthrough in the performance of photoelectrochemical hydrogen production.
Hydrogen energy has advantages such as zero carbon emissions, green characteristics, and high energy density, which are of great significance in achieving carbon peak and carbon neutrality goals. This year, hydrogen energy industry was mentioned for the first time as a frontier emerging industry in the "Government Work Report," marking it as one of the important directions for developing new productive forces.
The key to the comprehensive rise of the hydrogen energy industry lies in reducing the cost of green hydrogen production. Photoelectrochemical water splitting technology can directly convert intermittent solar energy into hydrogen energy, making it a highly promising renewable energy technology. Cu2O, as a natural p-type semiconductor, has advantages such as abundant raw material reserves, simple preparation methods, a relatively narrow bandgap, and suitable energy level positions, making it a "star" material for efficient and inexpensive photoelectrochemical hydrogen production electrodes.
In improving the photoelectrochemical performance of Cu2O, enhancing the separation and transport efficiency of photo-generated charge carriers is crucial. Currently, there is limited research in the academic community on the recombination process of charge carriers within Cu2O bulk phase.
To reveal the mechanism of the influence of different crystal orientations on the recombination of charge carriers within the Cu2O bulk phase, Professor Luo Jingshan's team from Nankai University, in collaboration with research teams from the University of Cambridge and the Swiss Federal Institute of Technology in Lausanne, used solution-phase epitaxial growth technology for Cu2O thin films and successfully prepared single-crystal Cu2O photoelectrodes with [111], [110], and [100] crystal orientations.
Subsequently, the team analyzed the photoelectrical properties of Cu2O photoelectrodes with different crystal orientations. The results showed that the carrier mobility, conductivity, and carrier diffusion length along the [111] crystal direction of single-crystal Cu2O were relatively superior, demonstrating a relatively higher photocurrent density.
a. Electrochemical epitaxial growth setup; b. X-ray diffraction pattern of single-crystal epitaxial layer on Si substrate and pole figures generated by EBSD (c), with reflections highlighted by circles; transient reflectance spectra of 15 nm single-crystal Cu2O thin films with crystal orientations of (100) (d), (110) (e), and (111) (f); current density-voltage response curves of traditional polycrystalline Cu2O and [111]-oriented enhanced polycrystalline Cu2O photoelectrodes [poly-Cu2O (111)] under simulated solar AM1.5 G illumination (g); stability test and hydrogen production Faradaic efficiency of poly-Cu2O (111) photoelectrode at 0.5 V (vs. RHE) (h).
Based on the analysis results, the team successfully prepared polycrystalline Cu2O photoelectrodes with high-purity [111] crystal orientation, demonstrating the advantages of electronic properties in the [111] direction, ultimately increasing the photocurrent density of the Cu2O photoelectrode at 0.5 V (vs. RHE) to 7 mA cm-2 (a 70% improvement over the previous electrodeposition photoelectrode).
Furthermore, the team investigated the influence of different crystal orientations and corresponding exposed facets on the stability of Cu2O photoelectrodes, revealing that the [111] crystal orientation and (111) crystal face termination provided the Cu2O photocathode with superior stability.
It is reported that this achievement innovatively developed a solution-based electrochemical epitaxial growth technique for preparing single-crystal Cu2O thin films, quantitatively analyzed the photoelectrochemical properties of Cu2O thin films with different crystal orientations, and revealed the impact of different crystal orientations on the behavior of bulk carrier recombination.
Based on these findings, the team enhanced the [111] crystal orientation of polycrystalline Cu2O photoelectrodes, thereby improving the photoelectrocatalytic performance of planar Cu2O photocathodes. These discoveries provide a widely applicable strategy for enhancing the modification of oxides in the fields of photovoltaics, transistors, detectors, and solar fuels.
Related paper link: https://www.nature.com/articles/s41586-024-07273-8
