Francisco Trinidad
Agenda for
5-9 September
2022
Bio
Francisco Trinidad holds an MSc and a PhD from the University of Madrid. In 1977, he joined the Tudor group and, following Exide’s acquisition of the company in 1995 finally became its Director of Battery Technology. Francisco’s present activities are to promote new technology approaches for lead–acid batteries via the use of different additives and the added value of alternative cell designs.
Carbon interacts with Lead reducing PbSO4 crystal growth during discharge and modifying the internal microstructure during charge by enlarging the electrochemically active surface area. As the specific surface area of Pb is lower than PbO2, the charge acceptance is usually limited by the negative electrode. Therefore, the electrochemical adsorption, deposition, and nucleation of Pb on carbon is quite important to create and sustain rechargeability of lead electrodes along the lifetime.
A wide range of carbon materials such as carbon black, graphite, activated carbon, graphene, carbon nanotubes and nanofibers have been used as additives to lead electrodes. These carbon materials show different affinities for Pb adsorption. Lead can be physically or electrochemically adsorbed on to carbon surface. Physical adsorption results from molecular condensation of lead compounds inside the capillaries of carbon materials. Electrochemical adsorption occurs when an electrical potential at the electrode-solution interphase is applied. As there is no straightforward relationship between surface area and lead adsorption efficiency, other factors like the presence of functional groups or dopants in the carbon surface need to be considered. Functional groups are known to create lead adsorption sites and enhance the wettability of carbon surface, which favours ionic adsorption, and improve lead electrodeposition efficiency.
Chemical and physical properties of carbon surface play vital roles both in lead ion adsorption and hydrogen evolution. Due to their low hydrogen over-potential, carbon may increase water loss, while the presence of other materials (such as Bi, Zn and organic surfactants) reduces it. Using lead compounds, as dopant for carbon additives, can effectively reduce hydrogen evolution. The presentation will explore different strategies to increase charge acceptance (by increasing the electrochemical active surface area of lead-carbon electrodes) while reducing water loss (by selectively modifying the surface properties to increase hydrogen over-potential).
