Structural Evolution in Photodeposited Nickel (Oxy)hydroxide Oxygen Evolution Electrocatalysts
Bibliographic record
Abstract
<div>Amorphous metal oxides expand the range of material parameters significantly compared to their crystalline counter parts. However, predictions of the exact nature of the amorphous phase and its effect on material properties are still elusive. Thorough structure-property investigations of well-known model systems are thus necessary before predictive control of useful material properties is obtained. In this work, we fabricate a series of photodeposited nickel (oxy)hydroxide (NiO<sub>x</sub>) thin films and anneal them at temperatures up to 1000 <sup>o</sup>C. EXAFS, XRD and XPS are used to determine the local structure, allowing us to correlate it to measured electrochemical properties. We find an amorphous Ni(OH)<sub>2</sub>-like local structure for annealing conducted below 250 <sup>o</sup>C, followed by an amorphous-to-amorphous phase transition to a NiO-like structure by 300 <sup>o</sup>C, thus supplying evidence for different amorphous polymorphs in this Ni-O system. Above 400 <sup>o</sup>C a cubic NiO XRD diffraction pattern is detected. Electrochemically, we find a stepwise increase of the onset overpotential at this transition, indicating a change in potential-determining step and possibly OER reaction mechanism. The Tafel slope decreases linearly with annealing temperature, which we attribute to a decrease in (Ni)OOH reaction intermediary coverage, supported by <i>in-operando</i> UV-Vis electrochromism. Furthermore, we find that the (Ni)OOH coordination is increasingly strained with annealing temperature, which manifests in higher electrochromic coloring rates and lower binding energies. We identify this as the root cause of the lowered intermediary coverage. Thus, nano-crystalline NiO should kinetically be a superior catalyst to amorphous Ni(OH)<sub>2</sub>. However, at our benchmarking value of 10 mA cm<sup>-2</sup> the amorphous material exhibits lower overpotential, due to a combination of lower onset potential, large chemically active surface area and mass transport limitations under our conditions.</div>
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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) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| 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".