Influence of surface condition and agitation on the performance of pickled passivated stainless steel electrodes for water electrolysis

The performance of stainless steel electrodes in alkaline water electrolysis is strongly influenced by surface condition, interelectrode distance, and hydrodynamic regime. In particular, chemical surface treatments may alter the electrode/electrolyte interface and modify the global response of the cell. In this work, the influence of surface condition and agitation on the performance of pickled-passivated stainless steel electrodes were investigated in a two-electrode water electrolysis cell. 
 
Four anode/cathode surface configurations were studied: TL-TL, TL-PP, PP-TL, and PP-PP, where TL denotes the electrode under a cleaning treatment and PP the pickled-passivated one. The system was evaluated at interelectrode distances of 6, 10, 14, 18, and 22 mm, both in the absence and presence of agitation. Cell voltage-current density (V-j) curves were obtained, and the response was further compared at representative voltages of 2.5, 3.0, and 3.5 V. In addition, the effect of agitation was quantified through the parameter Δjagitation = jwith agitation − jwithout agitation. 
 
In the absence of agitation, interelectrode distance had a strong effect on performance, with current density decreasing systematically as the distance increased in all configurations. Under these conditions, the relative order of response was generally TL-TL > PP-TL > PP-PP > TL-PP, indicating that the pickled-passivated treatment did not improve the global cell response and that its effect depended on the electrode to which it was applied. In particular, treating only the cathode led to the least favorable behavior. To illustrate this trend with numerical values, at 3.0 V and 6 mm the abovementioned configurations presented current densities of 164.02, 145.93, 143.29, and 122.83 [mA cm?²] for TL-TL, PP-TL, PP-PP, and TL-PP, respectively. 
 
Under agitation, a markedly different behavior was observed. Although the effect of interelectrode distance remained evident, the relative order between configurations changed substantially. In general, the response tended to follow the order PP-TL > PP-PP > TL-PP > TL-TL, indicating that TL-TL became the least favorable configuration, while the systems containing at least one pickled-passivated electrode exhibited higher current densities over the full distance range. To illustrate this behavior numerically, at 3.0 V and 6 mm the current density values were 251.52, 246.36, 233.77, and 151.39 [mA cm?²] for PP-TL, PP-PP, TL-PP, and TL-TL, respectively. 
 
When the net effect of agitation was evaluated for each individual configuration as Δ????agitation = ????with agitation −????without agitation, a strong configuration dependence was observed. At 3.0 V and 6 mm, Δ????agitationwas −12.63 [mA cm?²] for TL-TL and +110.94, +105.58, and +103.07 [mA cm?²] for TL-PP, PP-TL, and PP-PP, respectively. In the treated systems, the positive effect of agitation remained significant at all distances, although it tended to decrease as the interelectrode gap increased. 
 
These results show that agitation not only changes the magnitude of the cell response but also modifies the hierarchy of performance among surface configurations. Agitation strongly favors systems containing at least one pickled-passivated electrode and attenuates the previously adverse effect associated with cathode treatment. Overall, the results highlight the importance of the interplay between surface condition, interelectrode distance, and agitation in determining the performance of stainless-steel-based water electrolysis systems.

María José Lavorante collaborates with the Research and Development Division of Renewable Energy at the Institution of Scientific and Technological Research for Defense (CITEDEF), Argentina. Her research interests include water electrolyzers, fuel cells, dark fermentation and conductometric titrations. She is Professor of Solids and Colloidal Chemistry at the Faculty of Engineering, National Defense University. From 2021 to 2024, she coordinated the CYTED H2Transel subnetwork “Electrolyzers for Industrial Use and Storage.” She has published numerous scientific articles in her areas of interest and has served as reviewer for international congresses and peer-reviewed journals.