Due to increasingly stringent environmental regulations for dealing with production residues, the purification of persistent residues have moved into research focus. Therefore, the inner recycling of process waters as a secondary raw material is getting continuously more relevant.

In search for new and efficient methods to purify process waters, electrochemical processes have moved to an aspiringly research emphasis. Especially electrochemical oxidation process are receiving much attention, in which strong oxidants are generated in situ, either directly on the electrode surfaces or indirectly, for instance through chemical trace substances (hypochlorite for example).

An innovative concept for removing trace elements is a combination of a boron-doped diamond electrode and a gas diffusion electrode (GDE) for generating highly oxidative species at both electrodes simultaneously. Such a system is not commercial available yet, which is mainly due to the absence of high efficient hydrogen peroxide generating gas diffusion electrodes working at greater current densities.

In addition to the challenging technical GDE design, the operating parameters strongly affect the electrochemical performance of H₂O₂-GDEs. While many published articles are screening electrodes under untechnical aspects with small Rotating-Ring-Disc-Electrode Systems [1, 2] or potential-controlled small scale electrolyzers [3, 4, 5], more technical-relevant scales under technical galvanostatic operation are missing.

Therefore, a technical-relevant scale of laboratory electrolysis with 100 square centimeters respectively was used, to evaluate the influence of process parameters to determine optimized operating points. The impact of current density, electrolytes pH-value, temperature (first results on the H₂O₂ concentration depending on temperature using 1 molar sodium hydroxide solution for a current density of 0.5 kA/m² are presented in the diagram below) and O₂ volume flow rate and the effect of the difference pressure were measured with respect to the H₂O₂-yield.

Finally, optimum process conditions for H₂O₂-producing GDE-evaluation are suggested.

References

1. J. F. Carneiro, R. S. Rocha, P. Hammer, R. Bertazzoli and M.R.V. Lanza, Applied Catalysis A: General, 517, 161–167 (2016).
2. W. R.P. Barros, R. M. Reis, R. S. Rocha and M. R.V. Lanza, Electrochimica Acta, 104, 12–18 (2013).
3. H. Luo, C. Li, C. Wu and X. Dong, RSC Adv, 5(80), 65227–65235 (2015).
4. R. S. Rocha, R. M. Reis, Beati, André A. G. F., M. R. V. Lanza, Sotomayor, Maria Del Pilar T. and R. Bertazzoli, Quím. Nova, 35(10), 1961–1966 (2012).
5. M. Panizza and G. Cerisola, Electrochimica Acta, 54(2), 876–878 (2008).