Electrodeposition of Dendritic Ni-Co Onto High-Voltage Electrodes of Electrostatic Particulate Matter (PM) Sensors

Abstract

Particulate matter (PM) or soot sensing technologies are needed for feedback and control of exhaust after-treatment systems to meet increasingly stringent environmental regulations. A novel low-cost electrostatic PM sensing approach has recently been developed based on a concentric electrode design with a central cylindrical high-voltage electrode surrounded by an inner baffle that serves as the ground/negative terminal. The sensing principle is not completely understood, but seems to rely on capturing naturally combustion charged particles on electrode surfaces where a delay in sensor startup time occurs during initial testing. The influence of three-dimensional dendritic Ni-Co coatings on PM sensor performance was examined. Nickel and cobalt were co-electrodeposited on cylindrical stainless steel substrates from an electrolytic bath using a square waveform cathodic current. The effect of altering the applied current density and the number of current cycles on the height and spacing of dendritic features was monitored in attempts to correlate surface morphology to the performance of the materials as PM sensors. Coatings were characterized using scanning electron microscopy and confocal laser microscopy, and Ni-Co coated cylinders were used as the central high-voltage electrodes of electrostatic PM sensors to determine the effect of different microstructures on sensor performance. The coated electrodes demonstrated an improvement in startup time for an optimized coating morphology when compared to bare control electrodes. The surface features of the dendritic Ni-Co coatings are believed to alter the interaction of PM with the high-voltage electrode and can induce a faster response of the sensor when optimal electrodeposition conditions are employed.