Temperature-Driven Mechanism Shift in RhRu₃Oₓ Catalysts Could Boost Water-Splitting Efficiency

RhRu3Ox catalyst mechanism under temperature variation

Scientists at Tohoku University in Japan have made a groundbreaking discovery about how temperature affects the performance and stability of one of the most promising catalysts for water-splitting reactions. Their study reveals that the catalyst RhRu₃Oₓ (rhodium–ruthenium oxide) changes its reaction mechanism depending on temperature, providing new insights into how to fine-tune catalysts for more efficient oxygen evolution reactions (OER) — a key process in clean hydrogen production.

Published in Nature Communications, this research sheds light on one of the most critical bottlenecks in electrochemical energy systems. The oxygen evolution reaction, part of the overall water-splitting process, often limits the efficiency of devices such as electrolyzers, fuel cells, and metal–air batteries. Understanding how catalyst behavior changes under operating conditions is essential for designing durable materials for large-scale green hydrogen generation.

Why Oxygen Evolution Reaction (OER) Matters

The OER plays a vital role in converting water into hydrogen and oxygen using electricity. While simple in concept, this reaction involves complex multi-electron transfers that require high energy input. The challenge for researchers is to develop catalysts that can efficiently accelerate these reactions while maintaining long-term stability under harsh electrochemical conditions.

Traditional catalysts — such as iridium and ruthenium oxides — are effective but costly and prone to degradation at elevated temperatures. To address these limitations, researchers have explored bimetallic and doped oxides that can alter electronic structures and improve durability. The RhRu₃Oₓ catalyst examined in this study is one such example, combining rhodium’s stability with ruthenium’s high catalytic activity.

Temperature as a Catalyst Tuning Parameter

The Tohoku team, led by Dr. Heng Liu and colleagues at the Advanced Institute for Materials Research (WPI-AIMR), used a specialized operando differential electrochemical mass spectrometry (DEMS) setup to observe how RhRu₃Oₓ behaves during oxygen evolution at different temperatures. Their results revealed a remarkable phenomenon: the reaction mechanism itself shifts depending on the temperature range.

At lower temperatures, the reaction proceeds mainly through the adsorbate evolution mechanism (AEM), where surface-bound intermediates gradually release oxygen. At higher temperatures, however, the process transitions to the lattice oxygen mechanism (LOM), where oxygen atoms from the catalyst lattice itself participate in the reaction.

This temperature-triggered mechanism switch alters both the kinetics and stability of the catalyst. By selectively activating either pathway, researchers can theoretically tune performance for specific applications — such as low-temperature electrolyzers for portable hydrogen generators or high-temperature systems for industrial-scale hydrogen production.

Operando Analysis and Long-Term Stability

The research team’s operando analysis — meaning experiments conducted under real operating conditions — allowed them to directly monitor oxygen isotope signals (O₂-32 and O₂-34) to track the source of evolved oxygen. This detailed measurement confirmed that higher temperatures encourage lattice oxygen participation, a process associated with faster reaction rates but potential structural degradation.

Despite this, the RhRu₃Oₓ catalyst demonstrated impressive durability, remaining stable for over 1,000 hours of continuous operation at room temperature under a high current density of 200 mA cm⁻². This result suggests that even as reaction pathways shift with temperature, the underlying catalyst architecture maintains remarkable integrity.

Computational Insights and Mechanistic Modeling

To complement their experimental findings, the team used first-principles calculations to map out Pourbaix diagrams — thermodynamic charts showing the stability of different surface species as a function of pH and potential. These computational models confirmed that temperature directly affects the free-energy barriers between AEM and LOM pathways, explaining the observed shift in catalytic behavior.

Such insights are crucial for rational catalyst design, allowing scientists to predict how atomic substitutions, doping, or surface reconstructions influence catalytic activity. The authors suggest that optimizing fluorine (F) doping levels in RhRu₃Oₓ could further enhance both its activity and long-term performance under commercial electrolyzer conditions.

Implications for Green Hydrogen and Beyond

This discovery represents a major leap forward in understanding the interplay between temperature, electronic structure, and reaction mechanisms in transition-metal oxide catalysts. By uncovering how heat alters reaction dynamics, scientists now have a new strategy for tailoring materials that balance both activity and durability — a key requirement for sustainable hydrogen technologies.

As nations accelerate their transition to renewable energy, efficient water electrolysis stands as one of the most promising routes for clean hydrogen production. Insights like these from Tohoku University not only improve catalyst design but also bring us closer to scalable, affordable solutions for the global energy challenge.

Original article: https://phys.org/news/2025-11-temperature-triggers-distinct-rhruo-reaction.html
DOI: 10.1038/s41467-025-64286-1

This article on Quantum Server Networks was prepared with the assistance of advanced AI technologies to enhance structure, readability, and SEO optimization for materials science audiences.

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