Balancing composition and phase stability in High-Entropy Metal Phosphates for proton conduction
- 1Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-Straße 2, Berlin, Germany, 12489
- 2Federal Institute for Materials Research and Testing (BAM, Richard-Willstätter-Straße 11, Berlin, Germany, 12489
Abstract
The transition to sustainable energy technologies necessitates the development of proton-conducting electrolytes free from critical raw materials. Transition metal phosphate octahydrates (vivanite and pakhmoskyite analogues) offer a promising structural platform for proton transport via the vehicle mechanism, yet their performance is typically dominated by specific cation identity, with cobalt-based systems serving as the benchmark. This study investigates a high-entropy design strategy to decouple proton conductivity from cobalt reliance by stabilizing complex solid solutions containing up to several distinct metal cations (Ni, Co, Fe, Mn, Mg, Cu, Cd, Zn) within the phosphate octahydrate framework. Using a low-temperature aqueous precipitation method, we successfully synthesized single-phase high-entropy metal phosphates (HEMPs) and systematically evaluated their proton conductivity at 25 °C and 80 °C. While binary and ternary systems often require high cobalt concentrations to maintain performance, high-entropy compositions demonstrate a synergistic effect where increased configurational entropy correlates strongly with enhanced conductivity. Statistical analysis using Random Forest and ridge regression reveals that at 80 °C, configurational entropy surpasses cobalt content as the primary driver of transport performance. This entropy-driven enhancement allows for the significant reduction of cobalt to ~ca. 40 mol% without compromising conductivity, with optimised systems achieving values comparable to or exceeding the pure cobalt benchmark. These findings validate the high-entropy approach as a viable pathway for designing sustainable, high-performance proton conductors, demonstrating that structural disorder can effectively compensate for the reduction of chemically specific but critical elements in functional materials.
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BibTeX
@misc{schwab2026balancing,
title = {{Balancing composition and phase stability in High-Entropy Metal Phosphates for proton conduction}},
author = {Alexander Schwab and Stephanos Karafiludis and Biswajit Bhattacharya and Ines Feldmann and Carsten Prinz and Franziska Emmerling and Tomasz M. Stawski},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15001395/v2},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15001395/v2},
note = {CC BY},
}
RIS
TY - UNPB
TI - Balancing composition and phase stability in High-Entropy Metal Phosphates for proton conduction
AU - Alexander Schwab
AU - Stephanos Karafiludis
AU - Biswajit Bhattacharya
AU - Ines Feldmann
AU - Carsten Prinz
AU - Franziska Emmerling
AU - Tomasz M. Stawski
PY - 2026
DA - 2026/10/14
PB - ChemRxiv
DO - 10.26434/chemrxiv.15001395/v2
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15001395/v2
AB - The transition to sustainable energy technologies necessitates the development of proton-conducting electrolytes free from critical raw materials. Transition metal phosphate octahydrates (vivanite and pakhmoskyite analogues) offer a promising structural platform for proton transport via the vehicle mechanism, yet their performance is typically dominated by specific cation identity, with cobalt-based systems serving as the benchmark. This study investigates a high-entropy design strategy to decouple proton conductivity from cobalt reliance by stabilizing complex solid solutions containing up to several distinct metal cations (Ni, Co, Fe, Mn, Mg, Cu, Cd, Zn) within the phosphate octahydrate framework. Using a low-temperature aqueous precipitation method, we successfully synthesized single-phase high-entropy metal phosphates (HEMPs) and systematically evaluated their proton conductivity at 25 °C and 80 °C. While binary and ternary systems often require high cobalt concentrations to maintain performance, high-entropy compositions demonstrate a synergistic effect where increased configurational entropy correlates strongly with enhanced conductivity. Statistical analysis using Random Forest and ridge regression reveals that at 80 °C, configurational entropy surpasses cobalt content as the primary driver of transport performance. This entropy-driven enhancement allows for the significant reduction of cobalt to ~ca. 40 mol% without compromising conductivity, with optimised systems achieving values comparable to or exceeding the pure cobalt benchmark. These findings validate the high-entropy approach as a viable pathway for designing sustainable, high-performance proton conductors, demonstrating that structural disorder can effectively compensate for the reduction of chemically specific but critical elements in functional materials.
ER -