Selective Hydrogen Evolution on Manganese Oxide Coated Electrodes: New Cathodes for Sodium Chlorate Production

Abstract

The safety and feasibility of industrial electrochemical production of sodium chlorate, an important chemical in the pulp and paper industry, depend on the selectivity of the electrode processes. The cathodic reduction of anodic products is sufficiently suppressed in the current technology by the addition of chromium(VI) to the electrolyte, but due to the high toxicity of these compounds, alternative pathways are required to maintain high process efficiency. In this paper, we evaluate the electrochemical hydrogen evolution reaction kinetics and selectivity on thermally formed manganese oxide-coated titanium electrodes in hypochlorite and chlorate solutions. The morphology and phase composition of manganese oxide layers were varied via alteration of the annealing temperature during synthesis, as confirmed by scanning electron microscopy, X-ray diffraction, synchrotron radiation X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure spectroscopy measurements. As shown in mass spectroscopy coupled electrochemical measurements, the hydrogen evolution selectivity in hypochlorite and chlorate solutions is dictated by the phase composition of the coating. Importantly, a hydrogen evolution efficiency of above 95% was achieved with electrodes of optimized composition (annealing temperature, thickness) in hypochlorite solutions. Further, these electrode coatings are nontoxic and Earth-abundant, offering the possibility of a more sustainable chlorate production.

Photoluminescent sea urchin-shaped carbon-nanobranched polymers as nanoprobes for the selective and sensitive assay of hypochlorite

“…Fig. S4 † illustrates the FL responses of the SUCNPs towards 500 mM ClO À at different pH values (5)(6)(7)(8)(9)(10); the optimal pH value is 7.0, so it was chosen for the following analysis.…”

Understanding selective thin films in the chlorate process

“…Although this is two orders of magnitude thicker than a similarly selective CrOx film [99], it is much thinner than the MnOx films deposited at more negative potentials, which still display markedly poorer reduction selectivity. The 150 nm film is also much thinner than the optimum found for ex situ thermally formed MnOx films, which is 2-3 µm [56]. The remarkable inhibition of films deposited at +0.9 V is not merely a function of film thickness but might also depend on composition and morphology.…”

“…Numerous alternative additives to dichromate have been proposed, including rare-earth metal (REM) salts [45]- [47], permanganate [55], [56], vanadate [57], and molybdate [49], [58]- [61]. Alloys of Fe and Cr were also investigated [43].…”

“…Of the alternatives to chromate proposed [40], [45], [46], [55], [74] MnOx containing films seem very promising owing to the fact that they can be deposited in situ from non-toxic permanganate solutions, and have shown very similar selectivity towards H2 production [55], [56]. MnOx is also used as a selectivity-inducing film for the oxygen evolution reaction [75].…”

“…Unlimited film growth would cause various problems in an industrial electrochemical reactor, ranging from larger resistances and higher cell potentials to short-circuiting and cell clogging [55]. However, a recent publication shows that thermally deposited MnOx films also induce excellent selectivity towards the HER in solutions containing hypochlorite [56].…”