Synergistically enhancing nitrate reduction into N₂ in water by N-doped Pd–Cu biochar bimetallic single-atom electrocatalysis

Highlights

1.	Excellent-active and N2 selective Pd–Cu-BC SACs were prepared through bamboo biochar;
2.	A typical three-dimensional electrocatalytic NO3-Nreduction system was proposed;
3.	N doping could reasonably modulate the electronic structure of Pd and Cu sites;
4.	Free radical (H*) played an important role in the nitrate electro-chemical reduction;
5.	Synergy between Pd and Cu in SACs could enhance NO3-N removal and N2 generation.

Abstract

Noble metal materials have been identified as high efficiency catalysts for electrocatalytic reduction of nitrate,  and the synthesis and manufacture of high catalytic activity and environmentally friendly catalysts of activating hydrogen for water purification applications is extremely attractive. In this work, the Pd–Cu single-atom catalysts (Pd–Cu-N-BC) were first prepared by direct growth of Pd–Cu single-atom on bamboo biochar by regulating the concentration of precursors and doping method, and then enhanced electrocatalytic reduction nitrate performance and N₂ generation. The results showed that Pd–Cu-N-BC displayed excellent catalytic activity and reusability in electrocatalytic reduction nitrate with a low potential of 0.47 V vs. RHE (@10 mA cm⁻²). The maximum nitrate removal efficiency and N₂ generation could reach about 100% and 72.32% within 180 min, respectively. The density functional theory (DFT) calculations confirmed that Cu atoms could catalyze the electrochemical reduction of nitrate to nitrite, and Pd atoms anchored in the nitrogen-doped biochar (N-BC) lattice could catalyze electrochemical reduction of nitrite to N₂ involving the formation of hydrogen radical (H*). The characterization results of XANES showed that electronic synergistic effect between Pd and Cu single atoms significantly promotes the N₂ production through hydrogenation while inhibiting the generation of byproducts, leading to significantly enhanced electrocatalytic reduction of nitrate to N₂. Finally, Pd–Cu-N-BC was designed as a 3D particle electrode for enhanced electrocatalytic reduction of nitrate, exhibiting excellent stability and reusability, which could be considered as a suitable candidate for applications in the remediation of nitrate contamination.

Funding

National Natural Science Foundation of China(52160017); the Chinese Postdoctoral Science Foundation(2019M650869)