To what extent can self-activating catalysts enhance hydrogen production in electrolyzers? Researchers at Johannes Gutenberg University Mainz (JGU) have investigated this question, and their findings were recently published in the renowned scientific journal Advanced Energy Materials. “These catalysts optimize themselves and improve over the course of operation,” explained Dr. Dandan Gao from the Department of Chemistry at JGU. “We are therefore convinced that they represent a new paradigm for hydrogen production.” In their review article, the researchers systematically consolidate, for the first time, the key characteristics of self-activation. To achieve this, they conducted a detailed analysis of 33 published studies on the oxygen evolution reaction and 17 studies on the hydrogen evolution reaction. In doing so, they not only quantified the performance improvements achieved with these new catalysts but also examined the underlying mechanisms and identified the driving forces behind the enhanced catalytic activity. “Self-activating electrocatalysts have the potential to advance scalable, cost-effective, and sustainable hydrogen production,” said Gao.

A holistic perspective on the reaction

Green hydrogen is produced using electrolyzers, which split water into hydrogen and oxygen at two electrodes with the help of renewable electricity. Catalysts ensure that this reaction proceeds as efficiently as possible. Self-activating catalysts, which coat the electrodes and may consist of a wide variety of substances, exhibit unique and highly interesting properties: their performance continuously improves during operation. “However, understanding of how the catalyst structure influences its performance has so far been limited,” said Gao. Most previous studies focused only on one half-reaction: the oxygen evolution reaction. “Our review is the first to examine both catalyst design for the oxygen evolution reaction and for the hydrogen evolution reaction,” Gao explained.

Changes in catalyst composition and structure

But why does the catalyst performance improve over time? Gao and her team discovered that diffusion causes the catalyst material to reorganize itself during operation. “Material from both the water and the electrode diffuses into the catalyst, and vice versa – meaning the different materials partially intermingle. This reorganization is one of the reasons for the increased efficiency,” Gao explained.

In addition, salts naturally present in water attack the surface of the electrocatalyst, making the surface more active and effective for the desired reaction. At the same time, not only do foreign materials penetrate the catalyst layer, but its nanostructure also changes – another factor contributing to the catalyst’s self-optimization. “The catalyst surface becomes rougher and therefore larger over time as a result of electrocatalysis. More active sites are exposed, which further enhances the catalyst’s efficiency,” said Gao.

Guidance for future research

In their publication, the researchers also look ahead to the near future. “To provide researchers with guidance for the next steps, we outline future directions based on current findings in order to accelerate sustainable hydrogen production,” said Gao. Where do knowledge gaps remain that should be addressed to enable scalable, cost-effective, and sustainable hydrogen production?

The researchers also establish a foundation for transforming today’s case-by-case analyses into standardized protocols, thereby making future research more efficient. For example, they propose standardized tables in which reaction mechanisms and key findings can be systematically documented.

New approaches: seawater electrolysis

Gao and her team also discuss new approaches to electrolysis using self-activating catalysts, including seawater electrolysis, where seawater is used instead of freshwater as the electrolyte. Normally, this is challenging because chloride ions present in seawater attack and damage conventional catalysts. In the case of self-activating catalysts, however, the attack of chloride ions on the electrode or catalyst surface can actually be beneficial. Instead of causing degradation, the ions can interact with the material surface in ways that improve both stability and catalytic efficiency. This is because the ions deliberately influence the electronic structure and reaction behavior of the material. “We hope to make self-activating catalysts ready for industrial application in the near future,” said Gao, “and thereby make hydrogen production more cost-effective and sustainable.”