Current density nanostructural materials

Experiments and simulations show that the characteristics of the nanostructures generated by this procedure are basically given by live parameters the distance between the STM and the substrate, the quantity of material loaded on the tip, the maximum ion current density for the dissolution of the material on the tip, the potential of the substrate, and the diameter of the STM apex. The controlled variation of these five parameters allows tailoring of the diameter and height of the clusters. 

Advances in nanostructured conducting materials for DET have resulted in impressive current densities for the ORR, and application of these three-dimensional materials to DET from MCOs other than CueO may provide biocathodes with the characteristics suitable for an implantable EFC. While a DET approach using MCOs can provide for ORR at potentials approaching the thermodynamic reduction potential for oxygen, the current density achievable in this approach still relies upon intimate contact, and correct orientation, ofthe MCO to a conducting surface. Use of a mediator, capable of close interaction with the TI site of the MCOs, and with a redox potential tailored to permit rapid electron transfer to the TI site, can eliminate the requirement for direct contact in the correct orientation between MCO and electrode, and offer the possibility of a three-dimensional biocatalytic reaction layer on electrodes for higher ORR current densities. 

The electrochemical synthetic techniques of nanostructured conducting polymers are mainly carried out using galvanostat, potentiostat, and cyclic voltammetry (CV)- The advantages of electrochemical over chemical preparation are that the sizes of the nano-particles are easily controlled by the applied potential, current density, scan rate, and the number of cycles, and especially that the nanostmctured conducting polymer deposited on the electrode material can be directly used to investigate its electrochemical properties and in situ spectroelectrochemical characteristics. 

CP nanomaterials can be synthesized by chemical or electrochemical methods. In chemical reactions generally powdery nanomaterials are produced and can be scaled up. Nanostructures of CP deposited on the electrode surface as films by electropolymerization have limited surfaces compared to the materials obtained by chemical synthesis. Nanostructures generally grow along the direction of the electric field to form oriented structures. The electrochemical polymerization reaction rate can be controlled through the applied potential or current density, and controlled amount of product can also be obtained. The morphology of the nanomaterials may also be modulated by the conditions of electropolymerization. Electrochemical polymerization is an... 

Figure 19.8 illustrates the effect of hold time at each current density point in MEA tests using different nanostructured thin film (NSTF) MEAs, showing increased MEA mass activity at 900 mV using 5 s holds (matching RDE values more closely) compared with lower MEA mass activity using 1,050 s holds at each point in the polarization curve [13] similar variations in activity between the MEA and RDE techniques may also be expected for core-shell catalyst materials. 

In order to be able to properly examine the inherent activity of minute amounts of OER catalysts, one needs a substrate with minimal interference, extremely slow OER kinetics of its own and extraordinary stability at high positive electrode potentials. The unique featiues of 3M s Pt-NSTF (nanostructured thin film) catalyst [12] such as superior durability, electrochemical inertness at high potentials, and the absence of corrosion interference due to exposed carbrui, made it a logical choice as a support [13, 14]. It is well known that pure platinum has a high overpotential for OER. For instance, at a current density of 1 mA/cm, the OER on platinum proceeds at a potential that is 0.47 V higher than oti single crystal ruthenium oxide [15]. Thus, the OER partial current density oti the Pt-NSTF substrate wiU be orders of magnitudes lower than on ruthenium, iridium, and other similar OER-active materials. 

In designing layered nanostructures, deposited material forms continuous layers but to achieve the same, deposition must take place in a very controlled manner. Moreover, factors such as temperature, pH of the electrolyte, electrolyte concentration, current density, and deposition time must be kept in mind as they greatly affect the quality of the material deposited. 

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