In our previous edition of #MeetOurPartners, we talked about the design of clean catalysts. Today, we revisit that topic from a different perspective and with a new protagonist. Let’s introduce our researcher Caillean Convery.
Convery is part of the ANEMEL team at the University of Newcastle upon Tyne, in the UK. He works in the Electrochemical science and engineering research group, led by Mohamed Mamlouk, responsible the development of fluorine-free membranes and the design of cleaner catalysts, using more abundant alternatives to precious metals like iridium and platinum. Further down the line, Newcastle will integrate both membranes and catalysts into a single setup. However, as Convery explains, “we haven’t really got that far yet, because we’ve been focusing first on the chemistry fundamentals.”
Our researcher certainly knows about chemistry and how to apply it to find solutions to different challenges. Previous to ANEMEL, he carried out a master’s degree in applied chemistry and chemical engineering at the University of Strathclyde in Glasgow, UK. Joining the project represented the best opportunity to combine the study of both hydrogen production— “It’s quite important for me because it’s the next step in the so-called energy transition,” he says— and the study of catalysts. Convery has now begun the third year of his PhD, just as we have entered the third year of our project.
Electrolysers consist of two separate electrodes: the anode and the cathode. The anode witnesses the oxygen evolution reaction (OER), and the cathode conducts the hydrogen evolution reaction (HER). Each side reaction requires different catalysts, due to distinct chemical requirements. “I am working on the oxygen evolution catalysts for seawater electrolysis and, specifically, I work on what are called metal coordination complexes as catalysts,” he says.
A metal coordination complex is a chemical compound consisting of a metal centre surrounded by organic molecules, made of other elements like carbon, nitrogen, hydrogen and oxygen. This is all at the atomic level, very tiny, so imagine a large molecule with a shiny core – the metallic centre. In Convery’s work, this centre is a metal known for its catalytic activity, and the surrounding coordination complexes help with its performance and stability. Typically, metals with catalytic properties include critical raw materials such as platinum, palladium, or iridium. However, at ANEMEL, we avoid using them due to their significant supply risks and high costs. Therefore, Convery is focused on earth-abundant metals like nickel, iron, and manganese.
Our researcher aims to maximise the efficiency of these OER catalysts. This means trying different combinations of coordination complexes and metals to achieve an optimal result. Here, Convery faces a few challenges. The first one is ensuring that the chosen compounds actually promote the OER.
“If they don’t work, that’s not necessarily a negative thing, because we also want to understand why,” he says. As he mentioned earlier, the group focuses on the chemistry fundamentals, which also involves studying the basic chemistry. But we can’t remain stuck on a complex that doesn’t work. Convery tests one metal centre at a time, but soon he will come up with creative combinations.
A key aspect is to measure the stability of catalysts in the harsh and corrosive conditions created by seawater electrolysis. “The primary challenge we face is the presence of chlorine. It competes with OER, the reaction we want to do in the first place, and corrodes our materials,” Convery explains. Chlorine corrodes the catalysts’ metals, which leaches metal ions into the solution and reduces the efficiency of the process. While platinum and precious metals stand strong, corrosion is an especially significant problem with the earth-abundant metals that Convery investigates. A possible answer involves coating the electrodes with other materials that have selectivity towards OER, while maintaining their electrical conductivity. In Convery’s words: “It’s trade-off, trying to find some middle ground between being stable and retaining their electrical conductivity.”
Convery uses several techniques for performing his initial screening for the materials. The basic two are cyclic voltammetry and linear sweep voltammetry. The first one of the most popular techniques in electrochemistry. It helps identify any oxidation peaks, which could be indicative of corrosion, shown as changes in the resulting electrical current. If this initial result is good, then the linear sweep voltammetry helps to judge how active the catalyst is.
For now, our researcher is still working on developing his best catalysts, and the first results are yet to come. As he says about direct seawater electrolysis, “there’s a reason that it’s not a done thing yet, and that’s that it seems like such a simple idea, but it’s not.”
References:
- N. Elgrishi et al. J. Chem. Ed. 2018, 95 (2), 197-206, DOI: 10.1021/acs.jchemed.7b00361
- J. Mohammed-Ibrahim and H. Moussab. Mater. Sci. Energy Technol. 2020, 3, 780-807, DOI: 10.1016/j.mset.2020.09.005
