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Balancing Iridium Speciation in Ir/NiO Single-Atom Catalysts for Overall Water Splitting
Yongfang Zhou1, Yu Mao1, Cuizhu Ye2
1School of Chemical Sciences, The University of Auckland, Auckland, New Zealand.
Small (Weinheim an Der Bergstrasse, Germany)
|July 29, 2026
Summary
Iridium single atoms on NiO nanosheets act as effective electrocatalysts for overall water splitting across all pH levels. This bifunctional catalyst demonstrates high efficiency for both oxygen and hydrogen evolution reactions, crucial for water electrolysis.
Area of Science:
- Materials Science
- Electrochemistry
- Catalysis
Background:
- Developing efficient electrocatalysts for overall water splitting is critical for clean hydrogen production.
- Existing catalysts often struggle with activity and stability across a wide pH range.
- Iridium-based catalysts show promise but require optimization for bifunctional activity.
Purpose of the Study:
- To design and investigate iridium single atoms supported on NiO nanosheets (Irx-NiO) as bifunctional electrocatalysts.
- To evaluate the performance of Irx-NiO for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) across alkaline, neutral, and acidic media.
- To elucidate the mechanism behind the enhanced bifunctional activity of Irx-NiO.
Main Methods:
- Synthesis of iridium single atoms supported on NiO nanosheets (Irx-NiO).
- Electrochemical characterization including overpotential measurements for OER and HER at 10 mA cm⁻² in various electrolytes (1.0 M KOH, 0.1 M PBS, 0.5 M H2SO4).
- Testing in an anion exchange membrane water electrolyser (AEMWE) to assess performance at high current density.
- Spectroscopic analysis and theoretical calculations to understand the role of iridium speciation and metal-support interactions.
Main Results:
- Irx-NiO catalysts exhibited low overpotentials for both OER and HER across different pH values.
- Ir8%-NiO demonstrated excellent bifunctional activity, requiring 177 mV (OER) and 29 mV (HER) in alkaline, 275 mV (OER) and 54 mV (HER) in neutral, and 174 mV (OER) and 24 mV (HER) in acidic media at 10 mA cm⁻².
- In an AEMWE, Ir8%-NiO achieved 1.0 A cm⁻² at 2.02 V with good stability.
- Spectroscopic and theoretical studies revealed that embedded and surface-adsorbed Ir atoms contribute synergistically to OER and HER.
Conclusions:
- Iridium single atoms supported on NiO nanosheets are highly effective bifunctional electrocatalysts for overall water splitting.
- The catalyst's performance is attributed to the dual role of embedded Ir in promoting OER and surface Ir in facilitating HER.
- Optimizing iridium speciation and metal-support interactions is key to achieving efficient water splitting across a broad pH range.
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