Boosting nitrate-to-ammonia electrosynthesis via hierarchically branched TiO2 nanorods

Abstract

Electrochemical nitrate reduction reaction (eNO₃RR) is a sustainable pathway for ammonia (NH₃) synthesis, yet it is often challenged by sluggish reaction kinetics and low product selectivity. Herein, we report the design and synthesis of hierarchical TiO₂ branched nanorods (BNRs) grown on carbon cloth (CC) through sequential hydrothermal and TiCl₃ solution treatments. This strategy yields a unique nanostructure possessing a high surface-to-volume ratio and abundant oxygen vacancies. Comprehensive structural and electrochemical analyses revealed that these TiO₂ BNRs possess significantly enhanced charge-carrier density and charge transfer efficiency compared to TiO₂ nanorods (NRs) and nanoparticles (NPs). Consequently, the TiO₂ BNRs dramatically boost NH₃ electrosynthesis, achieving a remarkable yield rate of 187.2 µmol cm⁻² h⁻¹ (corresponding to 37.44 µmol h⁻¹ mg_cat⁻¹ or 637.9 µg h⁻¹ mg_cat⁻¹) and a faradaic efficiency (FE) of 87.4% at −0.6 V vs. reversible hydrogen electrode (RHE) in 0.1 M NaOH with 0.1 M NO₃⁻. Furthermore, the TiO₂ BNR electrode demonstrated excellent operational stability over 50 h. This study highlights the profound impact of engineering hierarchical TiO₂ nanostructures for highly efficient eNO₃RR, advancing the prospect of sustainable ammonia production from nitrate-laden wastewater.