Palladium outperforms platinum for peroxide sensing in carbon nanotube hybrid

A recent study from the University of Sussex has highlighted the potential of multi-wall carbon nanotube (MWCNT) composite electrodes embedded with precious-metal blacks for electrochemical sensing. Researchers Fernando Perez, Chloe Miller, and Bhavik Anil Patel systematically compared platinum, palladium, and ruthenium blacks within these composites, finding that palladium black excels in detecting hydrogen peroxide, while platinum black is more effective for nitrite detection. This study, published in Results in Chemistry, suggests that a single catalyst cannot meet all sensing requirements, providing a framework for designing multi-analyte sensors.

Hydrogen peroxide and nitrite are critical targets for electrochemical sensors due to their biological and environmental significance. However, traditional carbon-based electrodes struggle with slow electron-transfer kinetics and low electrocatalytic activity, necessitating high overpotentials. To address these challenges, the Sussex team developed composite electrodes with 15 wt% MWCNTs and 10 wt% of either platinum, palladium, or ruthenium black, embedded in 75 wt% epoxy resin. This composition ensures mechanical stability and optimal electrochemical performance.

The study's findings emphasize the importance of precious-metal blacks in enhancing the electrochemical properties of MWCNT composites. Capacitance measurements and electrochemical impedance spectroscopy revealed increased capacitance and reduced charge-transfer resistance in all precious-metal black composites compared to unmodified MWCNT electrodes. These improvements indicate a larger electrochemically active surface area and better electron transfer.

For hydrogen peroxide detection, the palladium black composite demonstrated the highest sensitivity and lowest limit of detection, outperforming platinum and ruthenium blacks. Conversely, platinum black showed superior sensitivity for nitrite detection. The study attributes these differences to the unique adsorption energies and reaction kinetics of analyte-derived intermediates on palladium and platinum surfaces.

Scanning electron microscopy and energy-dispersive X-ray spectroscopy provided insights into the catalyst architecture, revealing that palladium black electrodes had a homogeneous particle distribution, while platinum black showed a mix of small particles and larger clusters. The ruthenium black electrodes exhibited the most heterogeneity, impacting their electrochemical performance.

The study also explored the application of these composites in glucose biosensors. Palladium black composites demonstrated superior performance in glucose oxidase-based sensing, with higher normalized current response and faster response times compared to platinum black. This performance is attributed to the efficient electrochemical detection of hydrogen peroxide, the enzymatic product in glucose biosensors.

Overall, the research establishes a versatile framework for designing electrochemical sensors with tailored precious-metal compositions and catalyst architectures. Palladium is recommended for peroxide detection, while platinum is preferred for nitrite, guiding the development of next-generation sensors.