A new dawn in hydrogen purification

Physics and chemistry journal Surface Science recognized ASU doctoral student Daniel Rivera for his work to prevent corrosion of palladium membranes

Across the U.S., many cars put out of service decades ago sit as shells of their former selves, their surfaces ruined by a reddish-brown crust. That crust is rust, formed by a relentless process in which iron reacts with oxygen in a chemical reaction, gradually corroding the metal. 

A similar challenge faces industries using palladium-based membranes for hydrogen gas purification. Discovered in 1802, palladium is a silvery-white metal widely used for purifying hydrogen. Purified hydrogen is a critical element in key industrial processes like, refining petroleum and semiconductor manufacturing.

Just as corrosion causes rust to ruin iron, chemical reactions between hydrogen sulfide and palladium also occur when using palladium-based membranes to purify hydrogen. 

Over time, the rate at which the membrane purifies hydrogen gets reduced due to a process called sulfur poisoning. 

Daniel Rivera, a chemical engineering doctoral student in the Ira A. Fulton Schools of Engineering at Arizona State University, developed a novel method using electric fields to prevent sulfur corrosion of palladium. Rivera’s work resulted in the physics and chemistry journal Surface Science naming him a runner-up for the 2023 Young Investigator Best Paper Award. 

Balancing purification efficiency and corrosion reduction

Users of palladium membranes currently prevent sulfur poisoning by changing the membrane’s chemical composition. Palladium is mixed with other metals such as copper, gold and silver to create an alloy to enhance the membranes’ resistance to hydrogen sulfide.

However, the alloys are not a foolproof solution. Their use presents  efficiency problems.

“The problem with alloying palladium with other metals is that none of them can achieve two crucial outcomes simultaneously — to reduce sulfur poisoning while maintaining or enhancing the rate at which hydrogen can pass through the membrane,” Rivera says. “Typically, an alloy might address one issue but not the other.”

Combining silver with palladium can make the membrane more susceptible to sulfur poisoning, but it allows hydrogen to pass through more rapidly. In contrast, integrating gold or copper with palladium can enhance the membrane’s ability to resist sulfur corrosion at the cost of slowing the speed at which hydrogen is purified. 

By observing how enzymes rely on electric fields to catalyze reactions, Rivera developed a hypothesis for using electric fields to prevent sulfur poisoning in palladium membranes while maintaining purification efficiency. 

“Hydrogen sulfide, much like water, is a bent molecule and has a dipole, which means it aligns in a specific orientation when subjected to an electric field,” he says. “The question I asked was, ‘Could we prevent hydrogen sulfide molecules from sticking to the palladium membrane surface by exposing it to electric fields?’” 

Considering the electric field’s direction — negative to positive — Rivera discovered that orienting a strong field toward the membrane surface could enable hydrogen to pass through and prevent sulfur corrosion on the membrane.

“The molecules might still come into contact with the surface, but the bond would be weak, making them move along for purification easily,” Rivera says. 

Rivera’s method has numerous applications beyond preventing sulfur poisoning of palladium membranes. He sees potential for a substantial number of uses in the petroleum industry.

“Petroleum refineries use around 26 million tons of hydrogen annually, and they produce it on-site through methods like steam reforming that turns methane into hydrogen,” he says. “This and other methods used are complex and require a lot of energy. Using palladium membranes would be simpler and save around 15% of the total hydrogen production energy budget, which has the potential to cut costs significantly.”

Among the challenges Rivera faced during his research, the biggest was finding an exceptionally strong electric field to validate his hypothesis.

Future purification plans

Rivera says being named a runner-up for the Best Paper Award is an honor and provides motivation to continue his research. He plans to delve deeper into the realm of palladium alloys, focusing on whether palladium-copper composites can exhibit similar purification efficiency to pure palladium when exposed to electric fields.  

Through his work, Rivera aims to contribute to solving critical global challenges in water safety and clean energy production. 

“I consider myself an environmentally conscious person,” he says. “Humanity is facing various issues; my goal is to apply my skills to help address some of them.”

He plans to contribute to providing safer water and a healthier environment using computational chemistry to design catalysts that can break down harmful contaminants like nitrates and per- and polyfluoroalkyl substances, or PFAS. 

Rivera’s choice to pursue his doctoral studies at ASU was influenced by the academic offerings in his field and his love for Arizona’s desert climate and landscape. 

“I applied to three universities, but I chose ASU because my advisor, Christopher Muhich, was the only faculty member whose work closely matched my research interests,” he says.

Muhich, an assistant professor of chemical engineering in the School for Engineering of Matter, Transport and Energy, part of the Fulton Schools, is excited for Daniel.

“Being recognized as the runner-up for the Surface Science Young Investigator Award is an amazing achievement,” says Muhich. “In various industries, enhancing palladium-based membranes’ resistance to poisoning without compromising their effectiveness is a significant challenge. Daniel’s findings that electric fields could prevent or reduce poisoning have the potential to be highly impactful.”