# Polymorphism-driven coordination geometry engineering for boosting nitrate electroreduction in Cu-pyrazolate chains

## TL;DR

Researchers engineered copper-pyrazolate structures to boost nitrate electroreduction efficiency by altering coordination geometry.

## Contribution

The study demonstrates that MOF polymorphism can precisely tune electronic structures for enhanced electrocatalytic performance.

## Key findings

- β-Cu(Pz)2 achieves 93.33% faradaic efficiency for nitrate reduction, surpassing α-Cu(Pz)2.
- Coordination geometry influences Cu electronic structure and nitrate activation through stronger Cu–O coupling.
- Cis-configuration in β-Cu(Pz)2 enables more delocalized Cu 3d orbitals, improving catalytic activity.

## Abstract

Tailoring the coordination geometry of metal centers through polymorphism offers a powerful approach to isolating the structural origin of catalytic activity in metal–organic frameworks (MOFs). Herein, two copper-pyrazolate (Pz) polymorphs, α-Cu(Pz)2 and β-Cu(Pz)2 were synthesized, featuring identical chemical compositions and 1-periodic chain structures but distinct local coordination configurations. Remarkably, the β-Cu(Pz)2 exhibits a faradaic efficiency (FE) of 93.33% for the nitrate reduction reaction (NO3RR), significantly outperforming α-Cu(Pz)2 (53.10%). Comprehensive structural analyses, in situ spectroscopy, and density functional theory (DFT) calculations revealed that the coordination geometry governs the electronic structure of the Cu active centers. Specifically, the cis-configured β-Cu(Pz)2 enables more delocalized Cu 3d orbitals and stronger Cu–O (NO3−) electronic coupling, thereby promoting nitrate adsorption and activation. This work demonstrates that MOF polymorphism allows precise tuning of electronic structures, offering a fundamental design principle for the development of advanced electrocatalysts toward sustainable nitrogen-cycle chemistry.

Coordination geometry-driven polymorphism in copper pyrazolates tailors Cu electronic structures, leading to highly efficient electrocatalytic nitrate reduction to ammonia with a faradaic efficiency of 93.3%.