# Electronic Interaction at Cu–O–Ni Heterointerface Promotes Electrocatalytic Nitrate Reduction to Ammonia and Zinc‐Nitrate Battery

## TL;DR

A new catalyst improves electrochemical conversion of nitrate to ammonia and powers a zinc-nitrate battery efficiently.

## Contribution

A Cu2O/Cu(OH)2@Ni(OH)2 heterostructure catalyst is developed with enhanced nitrate reduction and battery performance.

## Key findings

- The catalyst achieved 99.6% Faradaic efficiency and 1.14 mmol h−1 mg cat−1 ammonia yield in an H-cell.
- The Zn-NO3 hybrid battery reached 1.45 V open-circuit voltage and 6.47 mW cm−2 peak power density.
- The catalyst continuously produced 2.78 mg h−1 cm−2 ammonia with 93.6% efficiency over 24 hours.

## Abstract

Electrochemical nitrate‐to‐ammonia conversion powered by sustainable green electricity is a promising supplement to the traditional Haber–Bosch process, but it remains limited by low NH3 yield and Faradaic efficiency (FE). Herein, we report the synthesis and performance of a Cu2O/Cu(OH)2@Ni(OH)2 heterostructure catalyst. The interface exploits strong electronic interactions between Cu and Ni species, promoting efficient NO3
− adsorption and accelerating in situ water dissociation for hydrogenation steps. In an H‐cell, the catalyst achieved an FE of 99.6 % with an NH3 yield of 1.14 mmol h−1 mg cat−1, while a flow electrolyzer maintained 97.9 % efficiency and 17.13 mmol h−1 mg cat−1 at −600 mA cm−2. Via density functional theory (DFT) calculations and in situ characterization, the interface uses strong Cu–O–Ni electronic interactions to boost efficient NO3
− adsorption and accelerate in situ water dissociation for hydrogenation steps. When integrated as a cathode into a Zn‐NO3
− hybrid battery, the material served as a high‐performance cathode. The resulting battery's open‐circuit voltage reached 1.45 V, while its power density peaked at 6.47 mW cm−2. The integrated device continuously produced 2.78 mg h−1 cm−2 of NH3 with 93.6 % FE and exhibited robust stability (<2 % voltage decay over 24 h).

The strong Cu–O–Ni electronic interaction in the heterostructured catalyst can enhance the effective adsorption of NO3
− and accelerate the in situ hydrolysis dissociation of the hydrogenation step. The Zn‐NO3 hybrid battery assembled with this catalyst achieves an open‐circuit voltage of 1.45 V, a peak power density of 6.47 mW cm−2, and can continuously produce NH3 at a rate of 2.78 mg h−1 cm−2 with FE of 93.6 %.