Phase-Dependent Thermally Activated Self-Discharge of β-NiOOH and γ-NiOOH Electrodes
8 affiliations
- 1Grand Technion Energy Program (GTEP
- 2Technion - Israel Institute of Technology
- 3H2Pro, Ha-Tokhen St 2, Caesarea, Israel, 3079533
- 4Department of Chemical Sciences and Bernal Institute
- 5University of Limerick
- 6Department of Materials Science and Engineering
- 7Stewart and Lynda Resnick Sustainability Center for Catalysis (RSCC
- 8Technion – Israel Institute of Technology
Abstract
Nickel oxyhydroxide electrodes undergo spontaneous self-discharge that is strongly accelerated at elevated temperature. Although detrimental to alkaline batteries, this reaction is central to electrochemical–thermally activated chemical (E‑TAC) water splitting. The process operates in two distinct steps: electrochemical charging of Ni(OH)2 in cold (~25 °C) alkaline electrolyte and hydrogen generation at the cathode, followed by spontaneous regeneration of the charged NiOOH anode in hot (~80–100 °C) alkaline electrolyte, with concurrent oxygen evolution. A key unresolved question is how the charged-phase composition of NiOOH affects this thermally activated self-discharge. Here, we prepare phase-pure cobalt-doped β-NiOOH and γ-NiOOH electrodes using tailored electrochemical charging protocols and compare their short-term self-discharge in hot alkaline electrolyte simulating the TAC step in the E-TAC cycle. X-ray diffraction and iodometric titration show that phase-pure β-NiOOH undergoes little or no measurable structural or oxidation-state change after 5 min in 5 M KOH at 80 or 100 °C. In contrast, phase-pure γ-NiOOH exhibits substantial self-discharge, corresponding to 43-46% of the charge transferred during the preceding charging step, accompanied by partial transformation to α-Ni(OH)2. These results demonstrate that thermally activated self-discharge in charged nickel hydroxide electrodes is strongly phase-dependent under E-TAC-relevant conditions. More broadly, they show that γ-NiOOH, which is usually regarded as an undesirable overcharged phase in alkaline batteries, is closely associated with rapid chemical regeneration and therefore should be considered a key design variable in E-TAC anodes.
Related
- From hard carbon to activated carbon: influence of surface area and pore structure on the electrochemical performance of coconut rachis-derived supercapacitor electrodes
- Thermally Activated Delayed Fluorescence: An Extended Study of Peripherally Substituted DMAC‐TRZ Analogues
- Thermally activated delayed fluorescence in neutral and cationic stages of aza-nanographene decorated with 6.6.6 defects.
- A Terminal Carbazole Fused Ladder‐Type B,N‐Doped Multiresonant Thermally Activated Delayed Fluorescence Emitter: A Strategy for Deep‐Blue Emission
- Theoretical insights into the thermally activated delayed fluorescence of pyridazine derivatives: balancing twist and charge-transfer character
BibTeX
@misc{praznikov2026phasedependent,
title = {{Phase-Dependent Thermally Activated Self-Discharge of β-NiOOH and γ-NiOOH Electrodes}},
author = {Elena Praznikov and Avigail Varveri Landman and Avner Rothschild},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15008547/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008547/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Phase-Dependent Thermally Activated Self-Discharge of β-NiOOH and γ-NiOOH Electrodes
AU - Elena Praznikov
AU - Avigail Varveri Landman
AU - Avner Rothschild
PY - 2026
DA - 2026/09/09
PB - ChemRxiv
DO - 10.26434/chemrxiv.15008547/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008547/v1
AB - Nickel oxyhydroxide electrodes undergo spontaneous self-discharge that is strongly accelerated at elevated temperature. Although detrimental to alkaline batteries, this reaction is central to electrochemical–thermally activated chemical (E‑TAC) water splitting. The process operates in two distinct steps: electrochemical charging of Ni(OH)2 in cold (~25 °C) alkaline electrolyte and hydrogen generation at the cathode, followed by spontaneous regeneration of the charged NiOOH anode in hot (~80–100 °C) alkaline electrolyte, with concurrent oxygen evolution. A key unresolved question is how the charged-phase composition of NiOOH affects this thermally activated self-discharge. Here, we prepare phase-pure cobalt-doped β-NiOOH and γ-NiOOH electrodes using tailored electrochemical charging protocols and compare their short-term self-discharge in hot alkaline electrolyte simulating the TAC step in the E-TAC cycle. X-ray diffraction and iodometric titration show that phase-pure β-NiOOH undergoes little or no measurable structural or oxidation-state change after 5 min in 5 M KOH at 80 or 100 °C. In contrast, phase-pure γ-NiOOH exhibits substantial self-discharge, corresponding to 43-46% of the charge transferred during the preceding charging step, accompanied by partial transformation to α-Ni(OH)2. These results demonstrate that thermally activated self-discharge in charged nickel hydroxide electrodes is strongly phase-dependent under E-TAC-relevant conditions. More broadly, they show that γ-NiOOH, which is usually regarded as an undesirable overcharged phase in alkaline batteries, is closely associated with rapid chemical regeneration and therefore should be considered a key design variable in E-TAC anodes.
ER -