Splicing the active phases of copper/cobalt-based catalysts achieves high-rate tandem electroreduction of nitrate to ammonia

Abstract

Electrocatalytic recycling of waste nitrate (NO3−) to valuable ammonia (NH3) at ambient conditions is a green and appealing alternative to the Haber−Bosch process. However, the reaction requires multi-step electron and proton transfer, making it a grand challenge to drive high-rate NH3 synthesis in an energy-efficient way. Herein, we present a design concept of tandem catalysts, which involves coupling intermediate phases of different transition metals, existing at low applied overpotentials, as cooperative active sites that enable cascade NO3−-to-NH3 conversion, in turn avoiding the generally encountered scaling relations. We implement the concept by electrochemical transformation of Cu−Co binary sulfides into potential-dependent core−shell Cu/CuOx and Co/CoO phases. Electrochemical evaluation, kinetic studies, and in−situ Raman spectra reveal that the inner Cu/CuOx phases preferentially catalyze NO3− reduction to NO2−, which is rapidly reduced to NH3 at the nearby Co/CoO shell. This unique tandem catalyst system leads to a NO3−-to-NH3 Faradaic efficiency of 93.3 ± 2.1% in a wide range of NO3− concentrations at pH 13, a high NH3 yield rate of 1.17 mmol cm−2 h−1 in 0.1 M NO3− at −0.175 V vs. RHE, and a half-cell energy efficiency of ~36%, surpassing most previous reports.

Efficient Electroreduction of Nitrate into Ammonia at Ultralow Concentrations Via an Enrichment Effect

“…Notably, the j NH3 and FE NH3 values of Cu@C are comparable to those of the most advanced electrocatalysts for NO 3 − electroreduction at high concentrations (≥100 × 10 −3 m). [12,17,20,21,[25][26][27][28][29] The FE NH3 and yield rate of NH 3 for Cu@C with 100 × 10 −3 m NO 3 − decreased by only 3.8% and 13.4% after 20 rounds of successive reactions (Figure S16, Supporting Information).…”

Enhanced Activities in Alkaline Hydrogen and Oxygen Evolution Reactions on MoS2 Electrocatalysts by In‐Plane Sulfur Defects Coupled with Transition Metal Doping

“…The in situ Raman spectra of Co‐S v ‐MoS 2 show a peak at 479 cm −1 stemming from Co‐OOH/Co‐OH bonds (Figure S17, Supporting Information). [ 61,62 ] Figure 4e displays the corresponding Tafel slopes. Co‐S v ‐MoS 2 exhibits a Tafel slope of 128 ± 4 mV dec −1 , which is less than that of RuO 2 (145 ± 6 mV dec −1 ), suggesting superior OER kinetics possibly due to the large ratio of Co 3+ /Co 2+ .…”

Interfacial engineering of Cu–Fe2O3 nanotube arrays with built-in electric field and oxygen vacancies for boosting the electrocatalytic reduction of nitrates

“…45 Compared with Cu (932.4 eV and 952.2 eV for Cu 0 ), 46 the binding energy of Cu 0 in Cu–Fe 2 O 3 -60 appeared to have shifted slightly in the positive direction, indicating the decreased electron density of metal Cu in Cu–Fe 2 O 3 -60 due to electron loss. 47 Simultaneously, the slight negative shifts ( ca. 0.3 eV for Fe 2p 3/2 and 0.4 eV for Fe 2p 1/2 ) in the binding energy of Fe 3+ in Cu–Fe 2 O 3 -60 compared with CuO-Fe 2 O 3 (710.7 and 724.3 eV) suggested that Cu–Fe 2 O 3 -60 had gained electrons and become an electron-rich body on the Fe 2 O 3 side (Fig.…”