Electrochemical Cell for in-Situ Synthesis of Hydrogen Peroxide in Household Washing Machines

Abstract

Hydrogen peroxide (H2O2) is used as bleaching agent in household appliances like washing machines. For the bleaching of laundry with H2O2, an alkaline environment is required in the washing machine, which is ensured by the use of an heavy-duty detergent. In powdered heavy-duty detergents for washing machines, H2O2 is provided in form of sodium percarbonate, which releases H2O2 as soon as it is dissolved in water. As long-term stability of H2O2 in liquids requires acidic environment, no sufficient amount of H2O2 based bleach can be stored in liquid heavy-duty detergents, resulting in a lower bleaching efficiency for laundry cleaning. However, liquid heavy-duty detergents can be dosed fully automatically in washing machines, which is convenient for the user and can reduce the detergent consumption by optimizing dosing amount [1]. To take advantage of a fully automatic dosing system and at the same time obtain an effective heavy-duty detergent with bleach capability, an additional in-situ bleach source is required. An attractive route for the in-situ production of H2O2 is the electrochemical reduction of oxygen (O2) at a carbon-based cathode in a flow cell. The use of a gas diffusion electrode (GDE) results in higher production rates by directly supplying gaseous O2 to the reaction site compared to a submerged cathode where O2 is dissolved in the electrolyte [2,3]. As evidenced by the lack of literature, this kind of a specific application-related flow cell design for the use in a washing machine has not yet been developed.Therefore, a compact and simple electrochemical flow cell was developed that can provide sufficient H2O2 quantities within the time scale of a washing cycle and can be installed in a washing machine. The novel cell consists of an electrolyte reservoir, which is integrated within the cell and is separated from the dimensionally stable anode (DSA) by a divided wall. The expanded metal design of the DSA allows a zero gap arrangement by allowing the separator to lie directly on the anode. Between separator and carbon-based GDE, the electrolyte can be pumped in a circuit via the reservoir. A three-way valve allows the electrolyte accumulated with H2O2 to be discharged to the washing machine. The GDE is supplied with atmospheric O2 from the non-anode-facing side. During operation, the cell is first filled with electrolyte via the filling hole. As soon as the anode chamber (between the anode and the divided wall) is completely filled, the liquid can flow over the divided wall and fill the reservoir. Subsequently, the circulation pump and the air supply of the GDE are started and the current is applied. During electrolysis, the H2O2 is produced in the GDE and accumulates in the circulated electrolyte. The divided wall and the separator prevent the direct oxidation of H2O2 at the anode. The O2 produced at the anode can escape via the gas vent. After a sufficient amount of H2O2 has been generated in the electrolyte, electrolysis is stopped and the H2O2-solution is pumped into the drum of the washing machine via the 3-way valve.The transient H2O2 faradaic efficiency and energy consumption were compared to literature data. The combination of in-situ H2O2 production with liquid heavy-duty detergent was compared to a solid heavy-duty detergent using a standard soiled cotton textiles test.[1] Smulders, E. (2001), Laundry Detergents, Wiley-VCH; 1. Edition.[2] Pérez, J. F., et al. (2016), Electroch. Com. 71, 65–68.[3] Muddemann, T., et al. (2021), Proc. 9, 1482. Figure 1