Access to clean water is one of the UN’s strategic development goals. Though often seen to target mostly the developing counties or rural regions with low infrastructure, this is an important topic even in modern industrialized countries. Here, drinking water is certainly clean by most standards, yet it is often still contaminated with micropollutants with known adverse effects even at minute concentrations which are difficult to mitigate with conventional technology. Promising technologies to tackle this challenge include electrochemical or photoelectrochemical wastewater treatment, which can effectively completely mineralize organic pollutants using in-situ generated reactive oxygen species (ROS) like hydroxyl radicals.Photoelectrochemical wastewater treatment is an emerging technology for the removal of organic and inorganic pollutants from wastewater using sunlight as an additional or sole energy source and thereby saving on electricity costs. Since the water quality should not be subject to the intermittency of solar energy, we employ an additional conventional “dark” electrode which will operate with supplied external current in the absence of sufficient light energy. In particular, we use a BDD (boron-doped diamond) as anode in combination with a bismuth vanadate (BiVO4) based photoanode. In case of light illumination, this photoanode generates a photovoltage and current on its own without an external power supply. In both cases, ROS like hydroxyl radicals and hydrogen peroxide are formed from water oxidation. These two anodes are used in conjunction with a carbon-based gas diffusion electrode (GDE) as cathode. Here, atmospheric oxygen is reduced to form hydrogen peroxide also serving as oxidant.In addition to the described reactions, the electrolyte ions may also play an important role. These may form other peroxo-species at the electrodes themselves or indirectly via hydrogen peroxide and hydroxyl radicals. Recently, we could show that bicarbonate in particular plays a very important role, forming the highly potent peroxomonocarbonate which was shown about 200 times as active as hydrogen peroxide itself.[1] Overall, we show that the photoelectrochemical process can efficiently remove a wide range of recalcitrant pollutants from wastewater, including organic dyes, pesticides and pharmaceuticals. It has the advantage of being a sustainable and energy-efficient technology, as it uses sunlight as the primary energy source, meaning that a smaller amount of electricity needs to be fed in. We will further discuss the influence of the reaction parameters (light intensity, voltage, current density, pollutant concentration, flow rate) as well as the role the supporting electrolyte plays.[1] Schanz, T.; Burek, B. O.; Bloh, J. Z. ACS Energy Lett. 2023, 8, 1463–1467. Figure 1
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