Have chemists been optimising the wrong variable for years when it comes to dynamic catalysis? That’s the claim made in a new study out of the University of Houston, US.
‘A standard catalyst is “static” as it sits under fixed conditions and works at a set speed,’ explains Omar Abdelrahman at Houston. ‘A “dynamic” or “programmable” catalyst is actively shaken up, with its environment deliberately oscillated – for example, switching an applied voltage back and forth – to force it to work much faster.’
The conventional view is that a dynamic catalyst’s behaviour reflects how much time it spends in each state or oscillation. However, Abdelrahman and his co-author Atharva Burte found something different. ‘Time isn’t what matters most, but the extent of the reaction itself,’ Abdelrahman says. This means that what matters is how much reactant has already been converted into product, not the amount of time it’s spent reacting.
In the current study, the team’s experiments on the electro-oxidation of formic acid on a platinum surface showed that reaction rates and other kinetic parameters were governed by the fraction of chemistry occurring in each dynamic state, not the time spent in each.
‘In oscillatory catalysis, it is tempting to think in terms of duty cycle or time-averaged rates,’ comments Paul Dauenhauer at the University of Minnesota who was not involved in the study but has collaborated with Abdelrahman in the past. Dauenhauer notes that under dynamic catalytic conditions kinetic observables like apparent reaction order, activation energy and effective overpotential are better explained by how far the reaction has progressed than by how long it’s been running.
The insight first emerged from theory, Abdelrahman says, before being confirmed at the bench. ‘When we looked closely at the math governing how these catalysts respond to changing environments, the equations kept pointing back to the progress of the reaction rather than the ticking of a clock,’ he says. ‘When we went into the lab to verify this by measuring reaction barriers and behaviours experimentally, the data perfectly backed up the math.’
Their new framework also explains why dynamic catalysts need far less energy to achieve massive speedups than static ones. ‘The oscillation actually breaks the traditional limits of the surface, steering the chemistry down a less electrochemically controlled, highly accelerated pathway that one can’t access under normal, static conditions,’ adds Abdelrahman.
As their framework relies on fundamental principles of thermodynamics and kinetics, the duo expects it to be applicable across different types of energy inputs and timescales. If these findings extend to other systems, it could change how chemists design catalysts driven by changing electrical, light or mechanical inputs.
‘We want to use this framework as a blueprint to intentionally design next-generation catalyst systems rather than relying on trial and error,’ says Abdelrahman, ‘because the model can apply to light, mechanical stress or electricity, it could dramatically accelerate technologies vital to our transition to clean energy, such as generating hydrogen or engineering highly efficient fuel cells to tackle sustainability challenges.’
Dauenhauer cautions that dynamic catalysis will only be practical if the gains outweigh the energy needed to drive the oscillations, which could become substantial at industrial scale. ‘In an electrochemical system, for example, imposing rapid potential oscillations across a small laboratory electrode is very different from doing so uniformly across a large, porous, industrial electrode,’ he says.
