The electrochemical process of co-electrolyzing manganese metal and electrolytic manganese dioxide (EMD) is a sophisticated method aiming for dual product generation and improved energy utilization. Central to its success are the chemical additives that influence reaction kinetics, ion transport, and product morphology. NINGBO INNO PHARMCHEM CO.,LTD. is keenly interested in advancements that enhance this complex electrochemical dance, particularly the role of synergistic additive combinations like sodium sulfite (Na2SO3) and selenious acid (H2SeO3).

The core challenge in manganese co-electrolysis lies in balancing the cathodic reduction of manganese ions (Mn²⁺) to metallic manganese and the anodic oxidation of Mn²⁺ to electrolytic manganese dioxide (EMD). Additives are employed to fine-tune these reactions. Historically, selenium dioxide (SeO2) has been a staple, known for its ability to increase cathodic polarization, thereby suppressing the hydrogen evolution reaction (HER) and promoting efficient manganese deposition. However, the drive for sustainability necessitates reducing selenium usage.

Recent research provides a compelling case for the use of sodium sulfite as a complementary additive. When combined with a reduced concentration of selenious acid (H2SeO3), Na2SO3 exhibits a remarkable synergistic effect. Studies have identified optimal conditions, such as using 0.0175 g/L of H2SeO3 and 1.5 g/L of Na2SO3, which significantly elevate both cathodic and anodic current efficiencies. This enhancement is rooted in the electrochemical behavior imparted by these additives. Na2SO3, by acting as a reducing agent and influencing the electrolyte's composition, helps to create a more favorable environment for manganese deposition.

Electrochemical analyses, including cyclic voltammetry (CV) and linear sweep voltammetry (LSV), offer critical insights into these mechanisms. The presence of composite additives demonstrably alters the electrode potentials. For instance, the onset potential for manganese deposition shifts to a more positive value, indicating that manganese reduction becomes more favorable. This increased cathodic polarization, partly due to the adsorbed species from the additives, effectively redirects electrochemical current towards manganese plating rather than hydrogen gas evolution. The improved cathode polarization observed with Na2SO3 and H2SeO3 in combination is a key factor in achieving higher current efficiencies for manganese metal production.

Moreover, the study of ion transport behavior within the electrolytic cell reveals how these additives influence the overall process. While Mn²⁺ concentrations decrease in both compartments due to their intended reactions, the presence of Na2SO3 appears to manage the electrolyte composition and ion migration more effectively, contributing to the stability and efficiency of the process. The resulting manganese deposits are described as smooth and lustrous, with an α-type crystal structure, while the co-produced EMD shows uniform particle size and ε-type crystal morphology. These desirable material properties are direct consequences of the optimized electrochemical environment created by the composite additives.

At NINGBO INNO PHARMCHEM CO.,LTD., we understand that mastering the electrochemical nuances of such processes is vital. The successful integration of sodium sulfite with reduced levels of selenious acid offers a practical and scientifically grounded method to enhance the efficiency and sustainability of electrolytic manganese and EMD co-production, aligning with our commitment to advancing chemical technologies.