A key concept in catalysis is the “active site,” the location where the desired chemical transformation takes place. In the emerging field of electrochemical CO2 conversion, much attention had been focused characterizing the active sites on Cu, as this metal electrocatalyst can make ethylene, which is a key building block for the chemical industry.
In a paper published in ACS Catalysis, Chansol and Sydney have shown that this picture is incomplete. They discovered that the ability of Cu electrocatalysts to make ethylene and other C2 products is not due to the active sites alone. Instead, there is a critical role for “reservoir sites” which store a crucial reaction intermediate but do not convert it. In this sense, the reservoir serves as a supply chain for the active sites, effectively increasing their conversion rate.
According to Sydney, “”We found that intermediates like CO may be “world travelers,” with the ability to diffuse as far as the nanoparticle diameter before reacting or desorbing. Intermediate CO storage and supply pathways are governed by terrains of binding energy and local environments.”
This functionality is also found in biological chemical networks. David Savage, of UCB’s MCB Deparment, who was not associated with the study, notes the connection:
The surface catalysis reservoir is quite reminiscent of what we see in biological systems, such as the CO2 Concentrating Mechanisms in plants and bacteria, where CO2 is stored transiently prior to the actual reduction reaction. The biological systems use this molecular ‘sleight of hand’ in order to improve the kinetics and on-target specificity of the fixation reaction. It will be exciting to see if artificial systems can be extended to also exploit such a mechanism for catalytic improvements.