Carbonate-Induced Electrosynthesis of Hydrogen Peroxide via Two-Electron Water Oxidation.

Electrochemical synthesis of hydrogen peroxide (H2 O2 ), via the two-electron water oxidation reaction (2e- WOR), is an attractive method for the sustainable production of valuable chemicals in place of oxygen during water electrolysis. While the majority of 2e- WOR studies have focussed on electrocatalyst design, little research has been carried out on the selection of the supporting electrolyte. In this work, we investigate the impact of potassium carbonate (K2 CO3 ) electrolytes, and their key properties, on H2 O2 production. We found that at electrolyte pH values (>9.5) where the carbonate anion (CO3 2- ) was prevalent in the mixture, a 26.5 % increase in the Faraday efficiency (%FE) for H2 O2 production was achieved, compared to bicarbonate (HCO3 - ) dominant solutions. Utilising boron-doped diamond (BDD) in highly concentrated K2 CO3 solutions, current densities of up to 511 mA cm-2 (in 4 m) and %FEs of 91.5 % (in 5 m) could be attained. The results presented in this work highlight the influence of CO3 2- on electrochemical H2 O2 generation via the 2e- WOR and provide novel pathways to produce desirable commodities at the anode during electrochemical water splitting.

Electrochemical Disinfection of Dental Implants Experimentally Contaminated with Microorganisms as a Model for Periimplantitis.

Despite several methods having been described for disinfecting implants affected by periimplantitis, none of these are universally effective and may even alter surfaces and mechanical properties of implants. Boron-doped diamond (BDD) electrodes were fabricated from niobium wires and assembled as a single instrument for implant cleaning. Chemo-mechanical debridement and air abrasion were used as control methods. Different mono-species biofilms, formed by bacteria and yeasts, were allowed to develop in rich medium at 37 °C for three days. In addition, natural multi-species biofilms were treated. Implants were placed in silicone, polyurethane foam and bovine ribs for simulating different clinical conditions. Following treatment, the implants were rolled on blood agar plates, which were subsequently incubated at 37 °C and microbial growth was analyzed. Complete electrochemical disinfection of implant surfaces was achieved with a maximum treatment time of 20 min for Candida albicans, Candida dubliniensis, Enterococcus faecalis, Roseomonas mucosa, Staphylococcus epidermidis and Streptococcus sanguinis, while in case of spore-forming Bacillus pumilus and Bacillus subtilis, a number of colonies appeared after BDD electrode treatment indicating an incomplete disinfection. Independent of the species tested, complete disinfection was never achieved when conventional techniques were used. During treatment with BDD electrodes, only minor changes in temperature and pH value were observed. The instrument used here requires optimization so that higher charge quantities can be applied in shorter treatment times.

Influence of In-Situ Electrochemical Oxidation on Implant Surface and Colonizing Microorganisms Evaluated by Scanning Electron Microscopy.

Peri-implantitis is a worldwide increasing health problem, caused by infection of tissue and bone around an implant by biofilm-forming microorganisms. Effects of peri-implantitis treatment using mechanical debridement, air particle abrasion and electrochemical disinfection on implant surface integrity were compared. Dental implants covered with bacterial biofilm were cleaned using mechanical debridement and air particle abrasion. In addition, implants were disinfected using a novel electrochemical technique based on an array of boron-doped diamond (BDD) coated electrodes. Following treatment and preparation, the implants were inspected by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Mechanical debridement led to changes in surface topography destroying the manufacturer's medium-rough surface by scratch formation. Air particle abrasion led to accumulation of the abrasive used on the implant surface. With both treatment options, appearance of bacteria and yeasts was not affected. In contrast, electrochemical disinfection did not cause alterations of the implant surface but resulted in distorted microbial cells. Electrochemical disinfection of implant surfaces using BDD electrodes may constitute a promising treatment option for cleaning dental implant surfaces without negatively affecting materials and surface properties.