Bipolar membrane electrolyzers for co-upgrading of CO2 capture solutions and sulfide contaminants to syngas and sulfur

TL;DR

A new electrolyzer system uses bipolar membranes to convert CO2 and sulfide contaminants into syngas and sulfur efficiently.

Contribution

The study introduces a novel bipolar membrane electrolyzer that couples CO2 electroreduction with sulfur oxidation.

Findings

The system achieves low energy consumption with cell voltage under 2.5 V.

It enables high carbon utilization (>97%) and stable operation for over 300 hours.

Syngas with CO2 content below 3% and pure sulfur are continuously produced.

Abstract

Direct electrolysis of CO2 capture solutions (e.g. (bi)carbonate) streamlines upstream carbon supply, yet faces challenges including high cell voltage, low-value anode byproduct, and gaseous product impurity owing to incomplete CO2 utilization. Herein, we demonstrate a bipolar membrane (BPM) electrolyzer coupling CO2 capture solution reduction with sulfion oxidation reaction (SOR) for cogeneration of syngas and sulfur. Tailoring BPMs with rapid water dissociation kinetics and mass transfer facilitates paired reactions through pH gradients, with cathode acidification triggering in situ CO2 production for electroreduction while sustaining the alkaline environment necessary for anodic SOR. Leveraging gas–liquid extraction between the cathodic product stream and anolyte enables simultaneous syngas purification and sulfur precipitation, establishing a self-sustained system. With these material and process innovations, the paired electrolyzer achieves low energy consumptions (cell voltage <2.5 V), high carbon utilization (>97%), and long-term stable operation (>300 h) at 100 mA cm−2, continuously producing syngas (CO/H2 ratios = 2/1–1/1, with CO2 content <3%) and pure elemental sulfur.

This study pioneers a bipolar membrane-based electrolyzer that couples CO2 electroreduction with sulfur oxidation to simultaneously produce syngas and elemental sulfur from waste streams.

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