Molybdenum shows role in electrochemical hydride transfer

Platinum is the preferred catalyst for electrochemical hydride transfer - a chemical process for producing valuable chemicals or carbon-free fuels – but the metal is rare and expensive. Molybdenum - far more abundant and less costly - could potentially take platinum’s place in the process, Magnus Rueping and his team at KAUST (King Abdullah University of Science and Technology) have shown.

According to KAUST, several molybdenum-based catalysts, including molybdenum sulphide, have previously shown promise for hydride transfer electrocatalysis, but the reason for their high activity was unclear.

“We wanted to determine how this catalyst functioned,” said Jeremy Bau, a research scientist in Rueping’s lab.

The team applied electron paramagnetic resonance spectroscopy (EPR) to study the molybdenum sulphide electrocatalyst in real time. “Unexpectedly, we were able to capture the entire process as it was happening,” Bau said in a statement. “We were able to trap the catalyst’s active state: Mo³⁺ ions directly bound to hydrogen.”

The finding that molybdenum ions directly participate in hydride transfer could lead to improved catalysts.

“If we can demonstrate a cohesive theory for how molybdenum is responsible for hydride transfer activity, we can focus on improving molybdenum so that it can be competitive with platinum and also on developing new molybdenum catalysts as cheaper replacements for platinum,” Bau said.

One application of the catalyst could be to electrochemically split water molecules to produce hydrogen gas to turn renewable electricity into a storable, transportable fuel. However, the team also showed the catalyst had potential for empowering enzyme biocatalysts for green chemicals production.

In cells, enzymes often work with nature’s energy-carrier molecule NADH to catalyse reactions. However, NADH is prohibitively expensive for industrial biocatalysis. Electrochemically generated molybdenum hydride proved to be highly effective at regenerating NADH in situ in a biochemical reaction flask.

“We were surprised by the efficiency of the process,” Rueping said. “By-products are avoided and pure NADH is produced. Our discovery raises the possibility that the long-held goal of making chemicals through enzymes can be enabled by electrochemistry.”