Sharp Octahedral Nanostructures Boost Formic Acid Oxidation

Researchers have demonstrated that precise control over the shape of core-shell nanocrystals significantly enhances their ability to oxidize formic acid, a key reaction for direct formic acid fuel cells. Published in the journal Catal in August 2025, the study introduces CuNi@Pt-Cu nano-octahedra that outperform commercial platinum catalysts in specific activity and durability. The work addresses a persistent challenge in electrocatalysis: minimizing the use of expensive and scarce platinum while maintaining high performance in fuel cell applications. By leveraging a shape-directed synthesis protocol, the team created nanocrystals with sharp, well-defined edges that facilitate more efficient electrochemical reactions compared to their polyhedral counterparts.

The central finding of the study is that the octahedral morphology, dominated by (111) crystal facets, combined with interfacial lattice strain, drives superior catalytic performance. The authors synthesized these core-shell structures by growing a platinum-copper alloy shell over a copper-nickel octahedral core. This architecture allows for a “platinum-saving” design, where the precious metal is confined to an ultrathin outer layer, reducing overall material cost without sacrificing activity. The resulting nanocrystals exhibit a specific activity of approximately 25.2 mA/cm² for the formic acid oxidation reaction, a value that significantly exceeds that of commercial Pt/C catalysts, which recorded 4.36 mA/cm² under identical testing conditions.

Shape control in nanocrystal synthesis is notoriously difficult, particularly when adding a secondary shell to a pre-formed core. Previous attempts to create similar core-shell structures often resulted in morphological degradation, where the sharp vertices of the octahedra dissolved or became truncated during shell growth. The research team identified that high-energy sites at the corners and edges of the nanocrystals are more reactive and susceptible to dissolution. To overcome this, they optimized the reaction parameters, specifically employing a high reaction temperature of 240 °C, a rapid heating ramp of approximately 12 °C/min, and a slow injection rate of the platinum precursor. These conditions promoted the surface migration of platinum atoms, allowing them to redistribute evenly across the facets rather than accumulating at the edges, thereby preserving the sharp octahedral shape.

The synthesis process involved a two-step colloidal method. First, copper-nickel nano-octahedra were prepared as seed templates using a co-reduction technique with borane morpholine as the reducing agent. These seeds were then dispersed in a fresh colloidal solution containing oleic acid and oleylamine. During the second step, a solution of platinum(IV) chloride was gradually injected into the reaction mixture while the temperature was rapidly increased. The use of platinum(IV) chloride, rather than other platinum precursors, helped prevent heterogeneous nucleation and the formation of irregular structures. The final products were characterized using transmission electron microscopy and energy-dispersive X-ray spectroscopy, which confirmed the core-shell structure and the uniform distribution of platinum on the surface.

Electrochemical testing revealed that the shape of the catalyst plays a critical role in its performance. The CuNi@Pt-Cu nano-octahedra exhibited a peak current density of 25.2 mA/cm², which is approximately 5.75 times higher than the commercial Pt/C catalyst. In contrast, CuNi@Pt-Cu nanopolyhedra, which lack the defined octahedral shape, achieved a specific activity of only 15.7 mA/cm². This comparison highlights the importance of the (111) facets in promoting the direct oxidation pathway of formic acid to carbon dioxide. The direct pathway is preferred because it avoids the formation of carbon monoxide, a toxic intermediate that poisons platinum active sites and reduces catalyst efficiency over time.

The study also examined the stability of the catalysts through chronoamperometry tests. After one hour of continuous operation at their respective peak potentials, the octahedral nanocrystals retained 83% of their initial activity, showing only a 17% loss. In comparison, both the polyhedral counterpart and the commercial Pt/C catalyst suffered a significant activity loss of approximately 44%. This enhanced durability is attributed to the structural stability of the (111)-terminated facets, which are more resistant to surface poisoning and structural degradation.

Further analysis using CO stripping voltammetry demonstrated that the octahedral catalysts possess superior tolerance to carbon monoxide poisoning. The CO oxidation peak for the CuNi@Pt-Cu nano-octahedra occurred at 0.601 V, which is lower than the peaks observed for the polyhedral nanocrystals (0.615 V) and commercial Pt/C (0.620 V). This property is crucial for long-term fuel cell operation, where CO accumulation can lead to performance decay. The synergistic effects of ligand interactions, lattice strain, and well-defined morphology contribute to this enhanced CO tolerance.

The lattice strain at the interface between the copper-nickel core and the platinum-copper shell is another key factor in the improved performance. As a result, the direct oxidation pathway is favored, minimizing the accumulation of poisoning species. The authors suggest that this interfacial strain, combined with the shape effects, creates a robust platform for enhancing electrocatalytic activity while reducing platinum usage.

Long-term durability tests extended to six hours, with hourly electrolyte refreshment, further confirmed the stability of the octahedral catalysts. The CuNi@Pt-Cu nano-octahedra showed the slowest decay in specific activity, followed by the polyhedral nanocrystals and commercial Pt/C. The commercial catalyst exhibited continuous performance degradation even with solution renewal, highlighting the limitations of standard platinum catalysts in this application. The authors emphasize that while these results are promising, further studies under practical fuel cell operating conditions are necessary to fully assess the long-term performance and potential for real-world application.

The implications of this research extend beyond formic acid oxidation. By precisely controlling the synthesis parameters, researchers can tailor the surface facets and interfacial properties of nanocrystals to optimize their performance for specific applications. This work demonstrates the potential of multimetallic core-shell architectures to address the challenges of catalyst cost and stability in fuel cell technology.

The study underscores the importance of morphological control in nanocatalyst design. The ability to preserve sharp-edged octahedral morphology during shell growth is a significant technical achievement that enables the exploitation of shape-dependent catalytic effects. The findings provide a roadmap for developing cost-effective, high-performance platinum-based catalysts for direct formic acid fuel cells.

In conclusion, the synthesis of CuNi@Pt-Cu nano-octahedra represents a step forward in the development of efficient electrocatalysts for formic acid oxidation. The combination of shape control, interfacial strain, and multimetallic synergy results in a catalyst that offers both high activity and enhanced stability. While further optimization is required for practical fuel cell integration, the study highlights the potential of shape-directed nanocrystal synthesis to overcome the limitations of traditional platinum catalysts. This research contributes to the broader goal of reducing the reliance on precious metals while maintaining high catalytic performance in electrochemical energy conversion systems.

Subject of Research: Shape-directed CuNi@Pt-Cu nano-octahedra for enhanced formic acid electrooxidation

Article Title: Shape-directed CuNi@Pt-Cu nano-octahedra for enhanced formic acid electrooxidation

Article References: Li, C., Chen, X., Zhang, L., Zhao, B., Woolever-Frost, C., Bharathan, P., Dennett, A., Zhou, G., & Fang, J. (2025). Shape-directed CuNi@Pt-Cu nano-octahedra for enhanced formic acid electrooxidation. Catal, 1(1), Article 7. https://doi.org/10.1007/s44422-025-00007-5

Image Credits: AI Generated

DOI: 10.1007/s44422-025-00007-5

Keywords: Shape-directed, CuNi, Pt-Cu, nano-octahedra, enhanced, formic, acid, electrooxidation, scientific research