# Operando UV/vis Absorption Spectroscopy for Studying the Nitrate to Ammonia Conversion on Cu2O‑Based Electrodes

## TL;DR

This paper uses a new spectroscopy method to study how nitrate is converted to ammonia on copper-based electrodes and how the catalyst changes during the process.

## Contribution

The study introduces 2D-UV/vis SEC to simultaneously track reaction dynamics and catalyst transformation during nitrate reduction.

## Key findings

- Cu2O surfaces are mostly reduced to Cu0 under the selected electrochemical conditions.
- Higher nitrate concentrations hinder the reduction of nitrite, affecting the reaction pathway.
- 2D-UV/vis SEC provides detailed insights into both reaction intermediates and catalyst surface changes.

## Abstract

The electrochemical
conversion of nitrate to ammonia
was proposed
as a feasible strategy for ammonia production. However, a deep understanding
of the reaction mechanism and catalyst transformation is still needed
to reach real applications. Herein, operando 2D-UV/vis absorption
spectroelectrochemistry (2D-UV/vis SEC) was used to study in detail
the reaction dynamics, as well as the transformation of the catalyst
for the nitrate reduction to ammonia on Cu2O-based electrodes.
2D-UV/vis SEC combines two simultaneous UV/vis absorption spectroelectrochemistry
measurements to obtain information on a given system from two different
points of view: normal and parallel configurations. The UV/vis signal
in the parallel arrangement facilitates tracking of the reduction
of nitrate to nitrite, providing kinetic information about the process.
Conversely, the UV/vis signal in the normal configuration reveals
the transformation of the catalyst, providing more detailed information
about the changes occurring on the electrode surface during the reaction.
Spectroelectrochemistry responses have shed more light on the kinetics
of the process under the operating conditions. The results show that
at the selected potential window for nitrate reduction, the Cu2O surface is mostly reduced to Cu0, as evidenced
by the changes observed in absorbance in the normal configuration.
In addition, experiments performed at different initial nitrate concentrations
reveal that nitrite reduction is hampered by the nitrate concentration,
demonstrating the key role of the nitrate concentration in the reaction
pathway. This work highlights the usefulness of 2D-UV/vis SEC in untangling
the complex dynamics of the reaction intermediates and products as
well as the transformation of the catalyst surface in electrocatalytic
processes.