Electrode characteristics for ozone production: a case study using undoped and doped PbO2 on porous platinised titanium substrates

The primary aim of this paper is the study of the stability and electrochemical activity of PbO<inf>2</inf> electrodeposited onto porous, platinised Ti substrates. The evolution of O<inf>2</inf> from H<inf>2</inf>O oxidation, on as-prepared electrodes, results in the opening of large pores that effectively work as gas channels for removing O<inf>2</inf> generated inside the porous structure, thus favouring the reaction penetration deeper into the pores. A serious problem that limits the utilisation of the internal pore surface is the instability of PbO<inf>2</inf> towards corrosion at high positive potentials or currents. Occlusion of pores by corrosion products is clearly demonstrated by SEM analysis of electrodes after operation as O<inf>2</inf> evolving anodes. Doping PbO<inf>2</inf> with Fe³⁺ and Co²⁺ yields anodes that resist corrosion up to relatively high anodic potentials/currents; this extends the anode lifetime by decreasing amorphisation of the electrocatalyst and its partial detachment caused by a high pressure of O<inf>2</inf> formed inside the pores during water electrolysis. This is an important result since stability of electrodes is as important as their electrochemical activity for practical applications.In the domain of high positive potentials, PbO<inf>2</inf> doping by Fe³⁺ and Co²⁺ results in a significant increase of the current efficiency of ozone generation. The magnitude of the observed increase depends on the individual characteristics of the doping cation and of the electrolyte employed. Possible involvement of higher oxidation states of cobalt and iron in the reaction mechanism is discussed on the basis of published literature.