Excess greenhouse gas emissions and accelerating global warming pose an escalating risk to society. Among emerging mitigation pathways, electrocatalytic CO₂ reduction (CO₂RR) is widely viewed as a promising option for converting CO₂ into value-added chemicals and fuels. Realising this promise, however, depends critically on the rational selection and optimisation of the anodic reaction, which governs both the overall energy efficiency and the economic viability of the electrolyser. The oxygen evolution reaction (OER) is most often paired with CO₂RR at the anode, yet its high thermodynamic onset (≈1.23 V vs SHE) and sluggish kinetics make it energetically costly; in typical cells, OER can consume >90% of the electrical input while producing no salable co-product.

As an alternative, ethylene glycol (EG)—obtained by hydrolysing poly(ethylene terephthalate) (PET)—has gained attention as an anodic feedstock. PET is ubiquitous in packaging and textiles, with global consumption of ~28.45 Mt per year and a recycling rate of only ~23%, underscoring the need for more sustainable end-of-life routes [1]. Conventional mechanical recycling is energy-intensive and tends to downgrade material quality, whereas hydrolysis depolymerises PET back to monomers suitable for true recycling and even upcycling [2]. Coupling CO₂RR with EG oxidation (EGOR) offers a pathway to lower cell voltages while creating value on both electrodes [3]. Nevertheless, the literature on integrated CO₂RR + EGOR systems still faces key hurdles, including insufficient current densities and limited operational stability, highlighting the need for better anode/cathode interface engineering, transport management, and durability strategies.

We present a single, integrated electrolyser that co-processes hydrolysed PET and CO₂ to co-produce formate at ampere-scale rates. The anode employs a three-dimensional nickel-foam architecture to oxidise ethylene glycol (EG) obtained from PET hydrolysis [4]. By prioritizing mass transport and interfacial engineering rather than catalyst discovery alone, this anode delivers formate formation at 1.2 A·cm⁻²—to our knowledge, among the highest reported for non-noble metal systems. On the cathode, a Bi₂O₂CO₃-based gas-diffusion electrode (GDE) enables selective CO₂ electroreduction to formate, completing a closed-carbon valorisation loop within a single device.

The integrated design sustains 100 h of continuous operation at 0.50 A·cm⁻², maintaining Faradaic efficiencies of 93.7% at the anode (EG oxidation to formate) and 86.0% at the cathode (CO₂-to-formate). Operating membrane-free, the cell achieves a 2.91 V full-cell voltage at 1.0 A·cm⁻², corresponding to an energy input of ~0.10 kWh·mol⁻¹, a ~65% reduction relative to conventional benchmarks. These outcomes arise from deliberate electrode structuring—high-surface-area current collectors, controlled wettability, and optimised gas–liquid pathways—that collectively minimise concentration polarisation and ohmic losses.

Beyond demonstrating a practical route for simultaneous PET upcycling and CO₂ utilisation, this work clarifies design rules for integrated electrolysers: (i) choosing anodic reactions that generate value while lowering overall cell energy; (ii) engineering transport-centric electrodes to sustain high current densities; and (iii) leveraging cathode GDEs that stabilise key intermediates for selective CO₂-to-formate conversion. The platform provides a blueprint for coupling waste-derived organics with CO₂ electroreduction to manufacture commodity chemicals efficiently, offering a scalable pathway toward circular-carbon manufacturing.