SECM-induced localized electrochemical conversion of metal-organic frameworks into electrocatalytic metal sulfides

Metal organic frameworks (MOFs) are a family of high surface area materials composed of metal nodes coordinated with organic linkers.¹ Their unique properties generates a lot of research interest in many fields like gas storage and separation, and catalysis.¹ Generally, these materials are redox-inactive due to their electronically-insulating building blocks. In order to make them redox-active, three methods are being used i) utilization of redox-active building blocks in order to synthesize the MOF, ii) post synthetic introduction of redox active molecules by covalent or non-covalent interactions with the framework, and iii) using the MOF as a high surface area template to synthesize highly porous electrocatalytic active inorganic materials via high temperature thermal treatments.¹ Recently, we presented a new technique for room-temperature electrochemical conversion of MOF films (such as: ZIF-67 and Fe-MIL-88) into porous, electrocatalytically-active transition metal chalcogenide(CoS_x and FeS_x)².

Scanning electrochemical microscope (SECM) is a powerful tool for studying analytical electrochemical experiments such as electron transfer kinetics, mapping of surface electrochemical activity and the detection of electrocatalytic intermediates³. When working with a substrate-generation tip-collection mode, high collection efficiencies can also be achieved in SECM. However, to do so, one need to place two ultramicroelectrodes (UME) facing each other (substrate should have similar geometric surface area as the tip electrode)^4,5, Hence significantly adding to the preparation complexity of such experiments.

Here, we present a new method for localized and micro-patterned electrochemical conversion of MOF films (eg. ZIF-67) into electrocatalytic CoS_x with varying chemical compositions. By doing so, it will allow us engaging high-throughput study of the electrochemical activity of large number of catalyst compositions over a single electrode. Additionally, we could also overcome the fabrication complexity of UME platforms for measurements that require high collection efficiency. As such, we envision that our new method will pave the way for the design of improved electrocatalytic materials and their subsequent utilization in various energy-related applications.