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Artificial Synapse: Spatiotemporal Heterogeneities in Dopamine Electrochemistry at a Carbon Fiber Ultramicroelectrode
An artificial synapse is developed that mimics ultramicroelectrode (UME) amperometric detection of single cell exocytosis. It comprises the nanopipette of a scanning ion conductance microscope (SICM), which delivers rapid pulses of neurotransmitter (dopamine) locally and on demand at >1000 defined locations of a carbon fiber (CF) UME in each experiment. Analysis of the resulting UME current-space-time data reveals spatiotemporal heterogeneous electrode activity on the nanoscale and submillisecond time scale for dopamine electrooxidation at typical UME detection potentials. Through complementary surface charge mapping and finite element method (FEM) simulations, these previously unseen variations in electrochemical activity are related to heterogeneities in the surface chemistry of the CF UME.
Understanding how the bulk structure of a material affects catalysis on its surface is critical to the development of action-able catalyst design principles. Bulk defects have been shown to affect electrocatalytic materials that are important for energy conversion systems, but the structural origins of these effects have not been fully elucidated. Here we use a combi-nation of high-resolution scanning electrochemical cell microscopy and electron backscatter diffraction to visualize the potential-dependent electrocatalytic carbon dioxide ðCO2ÞI electroreduction and hydrogen ðH2ÞI evolution activity on Au elec-trodes and probe the effects of bulk defects. Comparing colocated activity maps and videos to the underlying microstructure and lattice deformation supports a model in which CO2 electroreduction is selectively enhanced by surface-terminating disloca-tions, which can accumulate at grain boundaries and slip bands. Our results suggest that the deliberate introduction of disloca-tions into materials is a promising strategy for improving catalytic properties.
Lifting the Lid on the Potentiostat: A Beginners Guide to Understanding Electrochemical Circuitry and Practical Operation
Students who undertake practical electrochemistry experiments for the first time, will come face to face with the potentiostat. To many this is simply a box containing electronics which enables a potential to be applied between a working and reference electrode, and a current to flow between the working and counter electrode, both of which are outputted to the experimentalist. Given the broad generality of electrochemistry across many disciplines it is these days very common for students entering the field to have a minimal background in electronics. This article serves as an introductory tutorial to those with no formalized training in this area. The reader is introduced to the operational amplifier, which is at the heart of the different potentiostatic electronic circuits and its role in enabling a potential to be applied and a current to be measured is explained. Voltage follower op-amp circuits are also highlighted, given their importance in measuring voltages accurately. We also discuss digital to analogue and analogue to digital conversion, the processes by which the electrochemical cell receives input signals and outputs data and data filtering. By reading the article, it is intended the reader will also gain a greater confidence in problem solving issues that arise with electrochemical cells, for example electrical noise, uncompensated resistance, reaching compliance voltage, signal digitisation and data interpretation. We also include trouble shooting tables that build on the information presented and can be used when undertaking practical electrochemistry.