Hexanuclear nickel-added silicotungstates as high-efficiency electrocatalysts for nitrate reduction to ammonia
Zhi-Hui Ni, Ning Liu, Chunhui Zhao, Liwei Mi
Abstract
Ammonia (NH<sub>3</sub>) is widely used in a wide range of fields since it has an extremely high energy density and is simple to liquefy and transport. Nitrate is also a source of pollution of the environment and drinking water sources. Therefore, there is a pressing demand for the design and production of high-efficiency catalysts for the nitrate reduction reaction (NO<sub>3</sub>RR). Herein, two nickel-added polyoxometalates (NiAPs),<strong> </strong>[Ni(en)<sub>2</sub>][Ni<sub>6</sub>(μ<sub>3</sub>-OH)<sub>3</sub>(en)<sub>3</sub>(H<sub>2</sub>O)<sub>6</sub>(B-<em>a</em>-SiW<sub>9</sub>O<sub>34</sub>)]<sub>2</sub>·6H<sub>2</sub>O (<strong>Ni<sub>6</sub>en</strong>) and [Ni(enMe)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>][Ni<sub>6</sub>(μ<sub>3</sub>-OH)<sub>3</sub>(H<sub>2</sub>O)<sub>6</sub>(enMe)<sub>3</sub>(B-<em>a</em>-SiW<sub>9</sub>O<sub>34</sub>)]<sub>2</sub>·8H<sub>2</sub>O (<strong>Ni<sub>6</sub>enMe</strong>) (en = ethylenediamine, enMe = 1,2-diaminopropane), were effectively synthesized under hydrothermal conditions that had a lot of electrons and were employed as e-NO<sub>3</sub>RR catalysts. The structures of the compounds were characterized by various instruments such as PXRD, IR, TGA, BET, SEM and XPS. The e-NO<sub>3</sub>RR tests were performed using electrochemical workstation. The results show that <strong>Ni<sub>6</sub>en</strong> and <strong>Ni<sub>6</sub>enMe</strong> have high-efficient electrochemical catalytic nitrogen reduction to ammonia. The highest NH<sub>3</sub> yield rate was 3.66 mg h<sup>−1</sup> mg<sub>cat.</sub><sup>−1</sup> for <strong>Ni<sub>6</sub>en</strong> with Faradaic efficiency (FE) of 89.32%, and the highest NH<sub>3</sub> yield rate was 3.46 mg h<sup>−1</sup> mg<sub>cat.</sub><sup>−1</sup> for <strong>Ni<sub>6</sub>enMe</strong> with FE of 86.75% at low voltage (-0.5 V vs. RHE), respectively. This discovery creates a novel path for manufacturing highly effective NO<sub>3</sub>RR electrocatalysts using metal-added polyoxometalate as the catalyst in ambient settings. The research's findings offer practical advice for creating effective electrocatalytic catalysts.