Palladium-alloyed titanium (grade 7) cathodes for sodium chlorate electrolysis: A combined structural and electrochemical study

This study compares commercially pure titanium grade 1 and palladium-alloyed titanium grade 7 as cathode materials for sodium chlorate electrolysis. Both materials were subjected to cathodic treatment at −300 mA cm −2 for up to 5 h in a synthetic chlorate liquor at 70 °C and evaluated using X-ray diffraction with Rietveld refinement, film-mode energy-dispersive X-ray fluorescence, and electrochemical measurements. After 5 h of cathodic treatment, Rietveld refinement identified 74.9(4) wt% δ-TiH 2-x in grade 1 and 28.2(3) wt% in grade 7, corresponding to a 2.7-fold lower crystalline hydride fraction in grade 7 under equivalent conditions. Film-mode EDXRF showed an increase in the Pd concentration within the near-surface sampling region of grade 7, from 0.196 ± 0.002 wt% to 0.240 ± 0.003 wt%. Electrochemically, grade 7 exhibited only minor open-circuit-potential variation during treatment and required cathodic potentials approximately 0.30–0.35 V less negative than grade 1 at current densities of −150, −250, and −300 mA cm −2 . Intrinsic HER kinetics and total hydrogen uptake were not determined. Using the measured cathodic potential differences, the assumed geometric cathode area, and the corresponding chlorate production rates, a preliminary cathodic energy-saving contribution of approximately 450–460 kWh per ton of chlorate was estimated. This estimate represents an order-of-magnitude calculation and should not be interpreted as a validated industrial prediction. Overall, the study provides an integrated structural, near-surface compositional, and electrochemical comparison of titanium grades 1 and 7, showing the concurrent occurrence in grade 7 of a lower crystalline hydride fraction, an increased near-surface Pd signal, and less negative cathodic potentials under the investigated conditions.