(Invited) High Efficiency Solar-to-Hydrogen Conversion on InGaN Nanowire Arrays
Bibliographic record
Abstract
Recently, III-nitride nanowire structures have been intensively investigated for applications in solar water splitting and hydrogen generation. Compared to the conventional oxide-based photoelectrodes, III-nitride nanowires offer distinct advantages including tunable energy bandgap across nearly the entire solar spectrum, conduction and valence band edges that can straddle water redox potentials under deep visible and near-infrared light irradiation , and high efficiency charge carrier separation and extraction. Spontaneous overall water splitting under UV, blue, and green light irradiation has been demonstrated on InGaN/GaN nanowire structures. Moreover, multi-band InGaN nanowire photocatalyst and photoanode have been developed to effectively harvest a large part of the solar spectrum . Such nanowire arrays also exhibit a high level of stability in aqueous solution . To further improve the efficiency of solar-to-hydrogen conversion, we have investigated the design, epitaxial growth, and testing of paired InGaN/GaN photoanode and photocathode. The devices exhibit relatively high incident photon-to-current conversion efficiency (up to 65%). The energy conversion efficiency in the wavelength range of 300-600 nm is also significantly improved, compared to a single electrode. Here, we report on the design principle and operation of such novel photoelectrodes. In this design, the photocathode and the photoanode are connected side by side, wherein the solar light can be split spectrally and spatially. Different split light spectra are spread out to strike the corresponding photoelectrodes. n -InGaN/GaN and p -InGaN/GaN decorated with Pt nanoparticles are used as the photoanode and photocathode, respectively. The design of paired InGaN nanowire photoelectrodes can provide high photovoltage without trading off on the harvesting of longer wavelength of sunlight. Catalyst-free, vertically aligned InGaN/GaN nanowire arrays were grown on n-type Si(111) substrate by radio frequency plasma-assisted molecular beam epitaxy under nitrogen rich conditions. After an in situ oxide desorption at ~ 770 °C, A GaN nanowire template with a height of ~ 200 nm was first grown on Si substrate. To enhance the carrier transport between the n -type Si substrate and p -InGaN nanowire, a tunnel junction consisting of n + -GaN/ p + -InGaN/ p + -GaN was implemented beneath the p -InGaN nanowire. The nanowires are doped n -type or p -type using silicon or magnesium, respectively. The photoelectrochemical (PEC) properties of the photocathode and the photoanodes were investigated separately using a cell with a three-electrode configuration in 1 mol/L HBr. A linear sweep voltammogram for n -InGaN/GaN photoanode was performed under both dark and illuminated conditions. The maximum incident photon-to-current conversion efficiency (IPCE) measured at 1 V vs. Ag/AgCl for the n -InGaN/GaN photoanode is ~ 50% at 350 nm, while the maximum IPCE for p -InGaN/GaN photocathode (at -0.6 V vs. Ag/AgCl) is ~ 65% at 350 nm. The IPCE shows a decreasing trend with increasing wavelength, limited by the effective light absorption of the nanowire structures. In the paired configuration, the incident light was split by using long- and short-pass optical filters. The parallel-connected photoanode was illuminated with light with wavelengths in the range of 300-480nm. The photocathode was illuminated with light with wavelengths of 485-600 nm. Using a two-electrode configuration, the photoanode was considered to be the working electrode, and the photocathode p -InGaN/GaN was connected as the counter electrode in 1 mol/L HCl. With this novel design, the power conversion efficiency in the range of 300-600 nm has been increased by nearly one order of magnitude, compared to efficiency of a single electrode. The maximum power conversion efficiency of this device can reach >5%. Work is currently in progress on the integration of InGaN nanowires with solar cells to achieve further increased efficiency for solar-to-hydrogen conversion.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".