Fabrication of Carbon-Platinum Interdigitated Array Electrodes and Their Application for Investigating Homogeneous Hydrogen Evolution Catalysis

Interdigitated array electrodes (IDAEs) with one carbon electrode and the other platinum electrode were constructed by electrodepositing platinum on one set of the carbon electrodes. Platinum deposition was confirmed by scanning electron microscope (SEM) and cyclic voltammetry. The width of the carbon and platinum digits is less than 2 μm and the gap between two adjacent digits is around 3 μm. The carbon-platinum IDAEs benefit from the characteristics of both carbon and platinum in that carbon can provide a wide nonreactive potential window while platinum is a good catalyst for hydrogen reactions making it useful to characterize the catalytic hydrogen production cycle of the molecular electrocatalyst [Ni(P Ph 2N Ph 2)2(CH3CN)](BF4)2 (where P Ph 2N Ph 2 is 1,3,5,7tetraphenyl-1,5-diaza-3,7-diphosphacyclooctane). With properly set potentials, the molecular electrocatalyst was reduced at the carbon digits to initiate a homogeneous H2 production reaction while the platinum digits detect the H2 by oxidation, providing direct evidence of its production rate from the catalytic cycles. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any Interdigitated array electrodes (IDAEs) contain two sets of closely spacedmicrobandelectrodesthatcanbeindependentlyoperatedatdifferentpotentialsallowingthemtosimultaneouslyperformbothreduction and oxidation reactions. The set of microband electrodes where the reaction is initialized is called the generator and the other set of electrodefingers is called the collector where products from generator can be measured (Figure 1a). The small geometric spacing between the electrode fingers (micron and sub-micron) results in an overlap of the diffusion layers of the generator and collector (Figure 1b) resulting in high collection efficiencies (the ratio of the limiting current on collector to the limiting current on generator), as high as 98%. 1,2 Due to their high sensitivity and collection efficiency, the IDAEs operated in a generation-collection mode are simple (since the structure and operation are relatively easy) and important tools and could be used as an alternative to the traditional rotating ring disk electrodes (RRDEs) for investigating electrochemical reactions and following chemical steps. In another word, the IDAE generator could be operated with controlled electron transfer reaction, while the collector receives the products from the generator, so as to provide more information about the reaction. Commercially available IDAEs are commonly made of platinum or gold, electrode materials that have a limited potential range (e.g. 0 to 0.9 V vs Ag/AgCl in HCl aqueous solution for Pt electrode) in aqueous solutions, 1,3‐7 but are used as biosensors 8‐17 and functionalized electrodes. 1,3‐7,18‐22 Besides Au and Pt IDAEs, carbon IDAEs are also being used and have great potential for electrochemical studies due to their non-catalytic properties and large potential range even in aqueous electrolytes. However they are not as widely utilized as metal IDAEs due to their limited commercial availability especially with small dimensions (< 5 μm digit sizes and gaps). Some research has been done on the fabrication, characterization and utilization of carbon IDAEs. 2,8‐17,23‐33 However, there are only a few reports where the two IDAE digits are fabricated from different materials allowing for new applications due to the different electrochemical properties of the two materials. ITO-Au IDAEs were developed and used to selectively detect dopamine without interference from ascorbic acid and uric acid. 5 A Pt-Hg IDAE was fabricated to simultaneously electrooxidize methanol on Pt generator and detect the reduction of the methanol oxidation product on the Hg collector. 34 A Au-Pt IDEA was used to selectively immobilize various redox species on one electrode. 35