Electrocatalytic Reduction of Nitrate Pollution and Electrocatalytic Oxygen Evolution Reaction from Water Resources

Abstract

Amid the pursuit of modernization, the urbanization process continues to advance, accompanied by rapid industrial and economic growth, the frequent occurrence of water resource abuse, pollution, and wastage. Water resource recycling stands as a crucial approach to addressing the water crisis, while the treatment of water pollution and the regeneration of water resources are of paramount importance. Groundwater, a vital freshwater resource, finds widespread application across nations worldwide. However, over the past few decades, contamination of groundwater by nitrate due to factors such as agricultural nitrogen fertilizer use, livestock industry growth, sewage irrigation, and domestic wastewater discharge, has emerged as a severe environmental concern. Furthermore, the oxygen evolution reaction (OER) at the anode during water electrolysis is relatively complex, requiring a significant overpotential. The development of high-performance OER catalysts to reduce the overpotential of OER and enhance energy conversion efficiency is crucial, especially in promoting the widespread adoption of water electrolysis technology within renewable energy systems. Hence, this thesis focuses on the treatment and conversion of nitrate pollution in water, as well as the reuse of transformed products, and investigates the oxygen evolution reaction (OER) at the anode during water electrolysis. The main contents are summarized as follows: (1) Electrocatalytic nitrate reduction reaction (NO3-RR) technology provides a promising solution to recover the nitrate nutrition from wastewater through catalyzing nitrate reduction into value-added NH3. However, the selectivity and efficiency of electrocatalysts are frustrated due to the imbalance of *H adsorption (for NO3 hydrogenation) and unavoidable adjacent *H self-coupling on active sites, resulting in competitive hydrogen evolution reaction (HER). This research report a PdCu single atom alloy (SAA) catalyst, that allows isolated Pd sites to produce *H for the hydrogenation process of *NO3 on neighboring Cu sites, which can restrain the *H self-coupling through extending the distance between two *H and thus effectively suppress competitive HER. Consequently, the PdCu SAA catalyst exhibits ultrahigh NH3 Faraday efficiency (FE) of 97.1% with a yield of 15.4 mol cm-2 h-1 from the electrocatalytic NO3-RR in the neutral electrolyte, outperforming most of the reported catalysts. (2) To date, electrocatalytic CO2 reduction in KHCO3 electrolyte is the closet technology to industrialization, but its long-term stability under industrial current density (>200mA cm-2) are severely limited by the counter reaction, oxygen evolution reaction (OER). This research focuses on Ru doped IrOx catalyst (IrOx/Ru) for OER in KHCO3 electrolyte under large industrial current density. The catalyst as anode electrocatalyst delivers a cell voltage of 3.9 V at 200 mA cm−2 for 500 hours exhibits boosted activity and ultrahigh stability. It can guide the design of future OER catalysts with high stability under large industrial current density in KHCO3 electrolyte, which is of great meaning for accelerating industrialization process of electrocatalytic CO2 reduction technology.