Cheap Copper-Aluminum Spinel Catalyst Shows Strong Performance for Splitting Water

Hydrogen produced from water has long been touted as a clean fuel of the future, but the bottleneck has always been the sluggish half of the reaction: the oxygen evolution reaction, or OER, which demands a large extra voltage before water molecules willingly give up their electrons and release oxygen gas. A research team working across institutions in Pakistan and Saudi Arabia now reports a low-cost candidate that could help change that calculus. In a study published in the journal Ionics, Muffarah Qasim, Sarah A. Alsalhi, Ali El-Rayyes, Wajih Ullah and colleagues describe a nanocomposite built from spinel copper aluminate, CuAl2O4, anchored on graphitic carbon nitride, a polymeric semiconductor better known as g-CN. The hybrid material, synthesized through a straightforward hydrothermal route, delivered an overpotential of just 235 millivolts for oxygen evolution in alkaline media, along with a Tafel slope of 47 millivolts per decade, figures that place it among the more competitive non-precious catalysts reported for this demanding reaction.

The appeal of the design lies in the marriage of two inexpensive components with complementary strengths. Spinel oxides, named for the crystal structure in which metal cations occupy tetrahedral and octahedral sites within a close-packed oxygen lattice, are prized in electrocatalysis for their robust frameworks and tunable electronic configurations. CuAl2O4 in particular brings a distinctive arrangement of copper and aluminum cations that, according to the authors, boosts OER activity by virtue of its unique electronic structure. On its own, however, a spinel oxide powder suffers from limited electrical conductivity and a tendency for particles to clump together, burying many of the active sites where the four-electron oxygen chemistry actually takes place. That is where the carbon nitride scaffold comes in.

Graphitic carbon nitride is a layered, graphite-like material made of carbon and nitrogen, typically produced by simply heating inexpensive nitrogen-rich precursors. It is chemically stable in both acids and bases, and its nitrogen-rich surface offers abundant anchoring points for metal species. In the new composite, the g-CN serves several roles at once. The researchers found that its incorporation increased the electrical conductivity of the hybrid, promoted rapid electron mobility between the oxide particles and the conductive support, and enlarged the electrochemically active surface area by encouraging the uniform dispersion of CuAl2O4. In practical terms, the carbon nitride keeps the spinel nanoparticles spread out and electrically wired, so that more of the catalyst surface participates in the reaction rather than sitting idle inside aggregates.

The synthesis itself is part of the story. The team used a hydrothermal method, a technique in which the reaction mixture is sealed in an autoclave and heated in water above its normal boiling point, allowing crystals and hybrid structures to grow under controlled conditions. Hydrothermal processing is economical, scalable and accessible to ordinary laboratories, which matters enormously for any catalyst hoping to compete with the incumbent technology. Today’s best OER catalysts are based on iridium and ruthenium, precious metals so scarce and expensive that they are widely viewed as impractical for the gigawatt-scale electrolyzers a hydrogen economy would require. A catalyst assembled from copper, aluminum and carbon nitride, all abundant and cheap, sidesteps that supply problem entirely.

The performance metrics reported in the study are worth unpacking for what they reveal about the catalyst’s behavior. The overpotential of 235 millivolts is the extra voltage beyond the thermodynamic requirement needed to drive a meaningful oxygen-evolving current; lower values translate directly into less wasted electricity and better energy efficiency for an electrolyzer. The Tafel slope of 47 millivolts per decade describes how quickly the current grows as voltage is increased, and it offers a window into the reaction mechanism, with smaller slopes generally indicating faster electron-transfer kinetics. A low solution resistance of 1.0495 ohms further indicates that the electrode and electrolyte impose little ohmic penalty, meaning less of the applied voltage is lost to internal resistance before it ever reaches the catalytic sites.

Perhaps the most striking number is the electrochemically active surface area, which the team measured at 587.5 square centimeters. ECSA, as it is abbreviated, estimates the true interfacial area where electrolyte, electrons and catalyst meet, and it is a key predictor of how much current a given mass of catalyst can deliver. The large value reflects the successful dispersion of the spinel phase on the carbon nitride support, confirming the morphological benefits the authors set out to achieve. The researchers characterized their samples thoroughly to establish these morphological, structural and textural features, building the case that the nanohybrid’s performance stems from genuine structural advantages rather than measurement artifacts.

Durability, the quiet killer of many promising electrocatalysts, also fared well. Alkaline water electrolysis is a punishing environment: the catalyst must withstand concentrated hydroxide solutions, continuous gas evolution that mechanically stresses the surface, and potential-driven reconstruction that can dissolve or transform active phases over time. The CuAl2O4/g-CN nanohybrid demonstrated extraordinary durability over 35 hours of continuous operation, according to the study, a result that suggests the carbon nitride support does more than boost activity; it also stabilizes the spinel particles against degradation. Long-term stability is precisely the property that separates laboratory curiosities from materials that could plausibly be engineered into real electrolyzer electrodes.

The work fits into a broader and rapidly growing effort to replace noble-metal OER catalysts with earth-abundant alternatives. Recent literature has explored perovskite oxides, transition-metal sulfides, layered double hydroxides and metal-organic framework derivatives, often coupled with carbon supports such as reduced graphene oxide or carbon nanotubes. Graphitic carbon nitride has emerged as a particularly versatile platform in this landscape, having been paired with nickel oxide, cobalt ferrite, ruthenium dioxide, cerium oxide and many other catalytic phases. The new study extends that strategy to a copper aluminate spinel, a combination that had received comparatively little attention as an OER catalyst, and demonstrates that the spinel-plus-carbon-nitride architecture can hold its own in alkaline media.

There are, of course, caveats that temper any immediate industrial claims. The reported measurements come from laboratory-scale three-electrode testing, and translating a powder catalyst into a full water-splitting device requires integrating it with a hydrogen-evolving cathode, optimizing catalyst loading and binder chemistry, and proving performance at the current densities commercial electrolyzers demand. The authors position their material as a viable catalyst for a variety of purposes, and the data support its promise as a sustainable alternative to rare noble-metal electrocatalysts, but scale-up studies and device-level demonstrations remain the necessary next steps. The team notes that the datasets generated in the work are available upon reasonable request, which should help other groups reproduce and build on the results.

Even so, the significance of the finding is easy to appreciate. Green hydrogen depends on splitting water with minimal energy loss, and every millivolt shaved off the oxygen evolution overpotential reduces the electricity bill of the entire process. By showing that a simple hydrothermal recipe can produce a durable, conductive, high-surface-area catalyst from copper, aluminum and carbon nitride, the researchers have added a compelling entry to the catalogue of non-precious OER catalysts. If follow-up work confirms the performance at scale, the humble combination of a spinel oxide and a carbon-based scaffold could move from the pages of Ionics toward the heart of the clean-energy infrastructure that the hydrogen economy will require.

Subject of Research: Development of a CuAl2O4/graphitic carbon nitride nanocomposite electrocatalyst for the oxygen evolution reaction in water splitting

Article Title: Spinel CuAl2O4 nanomaterials anchored on g-CN as an effective catalyst for water splitting

Article References: Qasim, M., Alsalhi, S. A., El-Rayyes, A., & Ullah, W. (2026). Spinel CuAl2O4 nanomaterials anchored on g-CN as an effective catalyst for water splitting. Ionics. https://doi.org/10.1007/s11581-026-07551-7

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07551-7

Keywords: water splitting, oxygen evolution reaction, electrocatalyst, CuAl2O4 spinel, graphitic carbon nitride, hydrothermal synthesis, green hydrogen, nanocomposite, alkaline electrolysis, overpotential, electrochemically active surface area, non-precious metal catalyst