The deoxygenation of aqueous media via oxygen reduction reaction
(ORR) in a membrane electrolysis flow system offers significant advantages
over alternative methods for removing dissolved oxygen. This study
demonstrates the efficacy of direct lignosulfonate oxidation on bare graphite
electrodes to achieve a rapid and significant decrease in dissolved oxygen
(DO) concentration through paired electrolysis. On the cathode, the catalyst
Pt/carbon paper is used for the oxygen reduction reaction (ORR) to attain
water as target product.
When applying 0.7 V bias, advantageously lower than required for water
splitting, the DO concentration that started at air-saturation (7.8 mg/l)
decreased during 30 min reaching a stationary level of 1 mg/l, while 70% of
O2 was reduced to H2O and 30% to H2O2. The faradic efficiency is estimated to
68%.
To suppress the crossing of lignosulfonate over the Nafion membrane,
removing the low molecular weights (< 3.5 kDa) lignosulfonate via dialysis
was attempted. However, the remaining higher molecular weight lignosulfonate
was significantly less electrochemically active compared to virgin lignin and
was not able to deoxygenate to as low DO.
The oxidation of lignosulfonate at room temperature in aqueous media
enhances the quinone content while preserving the structural integrity of the
biopolymer backbone. This method introduces a novel pathway for
lignosulfonate valorization and application.