A hydrogen radical pathway for efficacious electrochemical nitrate reduction to ammonia over an Fe-polyoxometalate/Cu electrocatalyst.

Electrochemical nitrate (NO 3 - ) reduction to ammonia (NH 3 ), which is a high value-added chemical or high-energy density carrier in many applications, could become a key process overcoming the disadvantages of the Haber-Bosch process; however, current electrocatalysts have severe drawbacks in terms of activity, selectivity, and stability. Here, we report the hydrogen radical (H*) pathway as a solution to overcome this challenge, as demonstrated by efficacious electrochemical NO 3 - reduction to NH 3 over the Fe-polyoxometalate (Fe-POM)/Cu hybrid electrocatalyst. Fe-POM, composed of Preyssler anions ([NaP 5 W 30 O 110 ] 14- ) and Fe cations, facilitates efficient H* generation via H 2 O + e - → H* + OH - , and H* transfer to the Cu sites of the Fe-POM/Cu catalyst enables selective NO 3 - reduction to NH 3 . O perando spectroelectrochemical spectra substantiate the occurrence of the H* pathway through direct observation of Fe redox related to H* generation and Cu redox related to NO 3 - binding. With the H* pathway, the Fe-POM/Cu electrodes exhibit high activity for NO 3 - reduction to NH 3 with 1.44 mg cm -2 h -1 in a 500 ppm NO 3 - /1 M KOH solution at -0.2 V vs. RHE, which is about 36-fold higher than that of the pristine Cu electrocatalyst. Additionally, it attains high selectivity with a faradaic efficiency of up to 97.09% at -0.2 V vs. RHE while exhibiting high catalytic stability over cycles.