(Invited) Diamond Electrodes for Electro-Chemical Synthesis

Abstract

Boron doped diamond (BDD) electrodes have remarkable electrochemical properties, they are enabling novel electrochemical processes, from advanced oxidation liquid waste treatment to new types of electrochemical sensors and emerging new environmental processes. As an allotrope of carbon the properties of diamond electrodes have been shown to be a function of their crystallinity, boron doping concentration and non diamond (graphitic) carbon content. Optimized solid free-standing (not a coating) electrodes with high crystallinity and heavily boron doped can have solvent windows > 4 V (versus SCE) combined with metal like conductivity. Many industrial chemical processes can benefit from the ability of diamond electrodes to deliver high oxidation and reduction potentials while suppressing the electrolysis of water. In the anodic region due to their high physical, chemical and electrochemical stability the hydroxyl and sulfate radical can be formed enabling direct or indirect electrochemical oxidation of dissolved species in the electrolyte. At the anode species such as nitrates can be reduced to nitrogen and since water electrolysis is suppressed in some conditions these processes can be carried out at near 100% Faraday current efficiencies Diamond electrodes are being used in electrochemical advanced oxidation processes (AOPs) for removal of recalcitrant organic pollutants in the industrial liquid wastes by mineralizing them to CO2 and H2. Hydroxyl radicals have a high oxidation potential (2.80V) when compared to ozone (2.08V) and hydrogen peroxide (1.27V) and since the formation takes place directly at the anode by electrochemical oxidation, these systems have been found to be highly effective and universally applicable. In environmental processing and recycling electro oxidation is emerging as a way of making closed cycle chemical processes for e.g. materials recovery from wastes and regeneration of process effluents. Diamond electrodes can be used to simultaneously remove dissolved organics contaminants and restore the oxidation potential of a process effluent. Enables a reduction of the need for chemical dosing and the disposal of chemical wastes. In this talk we will explore some examples of these new electrochemical processes and discuss the potential for new processes that exploit the cathodic properties of diamond electrodes.