# Porous Iridium Oxide Inverse Opal Catalysts Enable Efficient PEM Water Electrolysis

## TL;DR

This paper introduces a new type of catalyst for water electrolysis that uses less iridium while maintaining high performance, helping to make green hydrogen production more efficient.

## Contribution

The paper introduces porous iridium oxide inverse opal structures as unsupported bulk anode catalysts with superior performance in PEM water electrolysis.

## Key findings

- IrOx-IO anodes achieved 13 A cm⁻² at less than 0.1 gIr/kW with high efficiency.
- Porosity and surface area significantly influence electrochemical performance and stability.
- The study clarifies how catalyst morphology affects electrode reactivity in PEM-WE.

## Abstract

Green hydrogen produced by proton exchange membrane water electrolysis (PEM‐WE), has gained significant attention as a future energy carrier and as a feedstock for the chemical industry. Reducing the use of scarce iridium in PEM‐WE anodes is a critical requirement. In this work, porous iridium‐based inverse opal structures (IrOx‐IO) of varying pore sizes are introduced as novel unsupported bulk anode catalysts and their superior performance compared to commercial alternatives is demonstrated. The influence of porosity and surface area on the electrochemical performance is systematically investigated and categorized using voltage breakdown analysis and equivalent circuit modeling. Efficient IrOx‐IO operation requires balancing surface area and pore size, enabling high performance up to 13 A cm−
2 with iridium utilizations below 0.1 gIr/kW at 70% efficiency. The findings advance our understanding of unsupported bulk catalysts and, more importantly, expand the range of viable anode materials by clarifying how catalyst morphology influences electrode reactivity.

Porous iridium‐based inverse opal (IrOx‐IO) structures are introduced as high‐performance, unsupported PEM‐WE anode catalysts. Their electrochemical behavior is analyzed through porosity/surface area tuning, voltage breakdown, and circuit modeling. IrOx‐IO anodes reach 13 A cm−
2 at <0.1 gIr/kW with structural stability, offering enhanced iridium utilization and insights into morphology–performance relationships for future green hydrogen production.