The role of recombination catalysts in VRLA cells

Use of gas-recombining noble metal catalysts in valve regulated lead acid (VRLA) cells has added a new dimension to the design of these products. In standby ‘float’ operation, there appears be some difficulty in uniformly charging a VRLA battery string. This may be due to oxygen recombination promoting a depolarized negative that continues to self-discharge. While use of catalysts for VRLA cells has been explored for quite some time, realization that there is a lack of stoichiometry in oxygen and hydrogen evolution did not promote focused investigation in this direction. However, recent data shows that inserting a catalyst in the headspace changes the dynamics of the oxygen recombination reaction — recombination is suppressed at the negative plate and diverted to the surface of the catalyst. This changed dynamics overcomes the problem of negative self-discharge and ensures effective recharge of VRLA battery strings on float. This paper reviews the experimental work from C&D, which culminated in the commercialization of catalyst-equipped VRLA cells in long-life products. A laboratory device for investigating the quality of catalysts is also discussed.