The production of hydrogen fuel from water splitting through the hydrogen evolution reaction (HER) has been investigated for more than a century; yet, there exists no commercial water splitting device because of the lack of an efficient and cost-effective electrocatalyst. A new class of two-dimensional carbides and nitrides, known as MXenes, have been gaining popularity but still currently lack the performance necessary for large-scale implementation. In order to further enhance these materials, it is necessary to understand the mechanisms during electrochemical processes. In this presentation, I will report on the electrocatalytic performance of MXenes and show that these electrocatalysts are active for HER electrocatalysis. More specifically, I will show the report on the detailed mechanisms of HER electrocatalysis and charge storage mechanism on MXenes in acidic (HCl) and neutral (Na2SO4) electrolytes using in-situ/operando Raman spectroelectrochemical approach, which allows for real-time monitorization of the material under operating conditions. In acidic electrolyte, it is found that the HER mechanism proceeds through a surface protonation mechanism due to termination group changes, whereas neutral electrolyte HER undergoes an overcharging mechanism prior to splitting water to form hydrogen gas. For charge storage, it is found that acidic electrolytes allow for pseudocapacitive behavior to take place in a similar surface protonation mechanism as for HER. In neutral electrolytes, the charge storage mechanism follows a purely double layer capacitance mechanism with sodium ions adsorbing and desorbing from the surface. The new knowledge from this work can be applied to a broad class of materials and systems to advance the field of energy conversion and storage.

Elucidating MXenes’ catalysis and charge storage mechanisms using In-Situ/Operando Raman spectroelectrochemistry

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ACS Fall 2022

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