Tandem electrocatalytic-catalytic conversion of nitrate and waste polylactic acid to alanine

Herein, a tandem electrocatalytic-catalytic method is employed to produce valuable alanine from nitrate and waste polylactic acid (PLA). Initially, two strategies are proposed to enhance the performance of electrocatalytic NO₃⁻ reduction reaction (NO₃⁻RR): optimizing NO₃⁻ adsorption and accelerating water dissociation by modulating the cathode electrocatalyst. Fe-regulated Co nanosheets (Fe_0.33-Co(OH)₂ NSs) have been developed as an efficient electrocatalyst, which demonstrate a remarkable Faradaic efficiency (FE) of 98.2%, with a corresponding yield rate of 10.7 mg h⁻¹ cm⁻² for NO₃⁻RR to NH₃ at −0.1 V vs. RHE. Additionally, ∼95% FEs of NH₃ at −200 mA cm⁻² have been maintained for >430 h in the alkaline solution. Subsequently, in situ technologies have been utilized to elucidate the NO₃⁻RR pathways, the structure transformation of the electrocatalysts, and the effects of Fe-induced work function reduction and electron enrichment at Co sites on electrocatalytic activity. Finally, alanine is synthesized by using PLA and the generated NH₃ as the raw reactants on the Ru/TiO₂ catalyst, achieving maximum yield and selectivity of 81.3% and 91.8%, respectively, which provides a novel approach to utilize the nitrogen resource and mitigate plastic pollution.