# Development of Suppressed Ion Chromatography for the Online Quantification of Cations in Electrochemical Ammonia Synthesis Research

## TL;DR

A new ion chromatography method was developed to accurately measure ammonium in electrochemical ammonia synthesis experiments, revealing unexpected contamination sources.

## Contribution

A suppressed ion chromatography method with automated matrix neutralization was developed for precise ammonium quantification in acidic electrolytes.

## Key findings

- A detection limit of 2 µg L−1 ammonium was achieved using suppressed ion chromatography.
- Online ammonium measurements revealed Nafion ionomer as a significant contamination source.
- Prior production rates in ammonia synthesis may have been false positives due to contamination.

## Abstract

Practical research on the electrochemical nitrogen reduction reaction (eNRR) requires quantitative ammonia trace analysis because production rates are on the order of µg h−1 in aqueous electrolyte. This challenge is further aggravated by complex sample matrices. Ion chromatography is a powerful analytical technique for the quantitative determination of ammonium down to ppb‐concentrations, but requires matrix elimination (ME) for these kinds of sample. We developed a suppressed cation chromatography method using automated matrix neutralization and ME to quantitatively determine ammonium in 0.2 M sulfuric acid electrolyte at µg L−1 concentrations for use in NRR research. Although direct conductivity detection of cations is less sensitive than unsuppressed indirect conductivity detection, baseline noise requires suppression at these concentrations. Nonlinearity of the calibration curve became noticeable below ≈ 1 ng ammonium. A method limit of detection of 2 µg L−1 (ppbmol) for ammonium was achieved at 100 µL injection volume. Direct coupling of the electrochemical cell and IC enabled online quantification. This online measurement of ammonium in 0.2 M sulfuric acid electrolyte revealed ammonium contamination rapidly liberated from the hitherto judged negligible Nafion ionomer of the gas diffusion electrode at open circuit voltage, showing prior production rates to be likely false positives.

We developed a suppressed ion chromatography method with automated matrix neutralization and matrix elimination for the quantitative determination of ammonium in electrochemical ammonia synthesis research. Online determination of ammonium in 0.2 M sulfuric acid electrolyte revealed Nafion ionomer as a non‐negligible secondary source of ammonium contamination from airborne ammonia pollution.© 2026 WILEY‐VCH GmbH