New solar co-electrolysis route cuts green hydrogen cost below fossil hydrogen

This study presents a highly efficient approach to solar hydrogen production by pairing water electrolysis with the selective oxidation of biomass-derived glucose. Central to this advance is a copper-doped cobalt oxyhydroxide catalyst that guides glucose through a finely tuned cascade of α–C–C bond cleavages, producing up to 80% formate while simultaneously lowering the anodic potential by nearly 400 mV. This design enables hydrogen generation in a simple membrane-free reactor, achieving production rates that surpass 500 μmol h⁻¹ cm⁻². By converting low-cost sugars derived from non-food biomass cellulose into valuable chemicals during hydrogen generation, the method boosts energy efficiency and dramatically improves economic feasibility, pointing toward a more sustainable model for solar fuels.

As the world accelerates toward carbon-neutral energy systems, solar-driven water electrolysis has emerged as a cornerstone technology for producing clean hydrogen. Yet high operating costs — mostly tied to the energy-intensive oxygen evolution reaction — continue to hinder large-scale deployment. Biomass-derived sugars offer a compelling alternative reaction pathway: they oxidize more readily and create value-added chemical products. However, steering glucose away from over-oxidation and toward a single high-value product like formate has remained a fundamental challenge. Because of these challenges, there is a pressing need to explore catalysts capable of directing glucose along selective, energy-saving oxidation routes through carefully engineered reaction pathways.

A research team from China Agricultural University and Nanyang Technological University reported (DOI: 10.1016/j.esci.2025.100431) on May 26, 2025, in eScience that they have developed a copper-modified cobalt oxyhydroxide catalyst capable of cleanly converting glucose into formate while generating hydrogen at exceptionally high rates. Driven by an InGaP/GaAs/Ge triple-junction photovoltaic device, the membrane-free co-electrolysis system delivers over 500 μmol h⁻¹ cm⁻² of hydrogen. The work introduces a catalyst-guided cascade oxidation mechanism that substantially reduces energy input, opening new possibilities for integrating solar hydrogen production with sustainable biomass upgrading.

The researchers began by comparing earth-abundant metal oxyhydroxides and identified CoOOH as a promising starting point for glucose oxidation. They then systematically introduced various dopants and discovered that adding just 5 mol% copper transformed CoOOH into a far more selective and efficient electrocatalyst. With this modification, the yield of formate increased from 50% to 80%, and the onset potential for glucose oxidation dropped by about 400 mV, enabling highly energy-efficient co-electrolysis in alkaline conditions.

A suite of advanced characterization techniques, including X-ray photoelectron spectroscopy, Raman spectroscopy, electron microscopy, and in situ impedance analysis, revealed how copper reshapes the electronic landscape of the catalyst surface. Copper stabilizes reactive Co³⁺ sites while suppressing overly aggressive Co⁴⁺ species that typically lead to non-selective bond cleavage. Complementary DFT calculations showed that Cu doping disfavors side-on adsorption of glucose and suppresses β-cleavage pathways that form by-products. Instead, it promotes end-on binding at the aldehyde group, enabling a stepwise α-C–C cleavage sequence that releases formate from every carbon atom.

When paired with an earth-abundant Ni₄Mo cathode, the system produced pure hydrogen in a membrane-free cell with nearly 100% Faradaic efficiency. Under concentrated sunlight, the device achieved a hydrogen generation rate of 519.5 ± 0.4 μmol h⁻¹ cm⁻², maintaining stable performance across 24 hours of operation.

One of the study’s senior researchers noted that the findings illustrate how the catalyst design can reshape both the efficiency and economics of solar hydrogen production. By orchestrating glucose oxidation through a highly selective α-cleavage pathway, the catalyst not only reduces the electrical energy required but simultaneously upgrades biomass into a valuable chemical feedstock. This dual-function system, the expert emphasized, represents a pivotal shift toward more integrated and cost-effective renewable hydrogen technologies, demonstrating that sustainable chemistry and clean energy generation can be mutually reinforcing.

This co-electrolysis strategy offers a scalable and economically competitive route to green hydrogen by pairing energy-efficient operation with the sale of formate as a co-product. Economic modeling suggests that this approach could lower the levelized cost of hydrogen to $1.54 per kilogram, rivaling or undercutting hydrogen produced from fossil fuels. The membrane-free design also simplifies the system architecture and reduces capital costs, making industrial deployment more feasible. Importantly, the catalyst performs equally well on hydrolysates derived from agricultural waste, highlighting its compatibility with real-world biomass resources and its potential to support distributed hydrogen production in future circular bioeconomy systems.

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