Precious-metal black carbon nanotube hybrid nanomaterial for sensitive detection of hydrogen peroxide and nitrite

The direct electrochemical detection of hydrogen peroxide (H 2 O 2 ) and nitrite remains challenging on carbon-based electrodes due to slow electron-transfer kinetics, high overpotentials, and limited intrinsic electrocatalytic activity. Precious-metal-black materials provide high surface areas and favourable catalytic properties, yet their standalone use is hindered by poor structural stability. Here, we fabricate and evaluate three precious-metal-black/multi-wall carbon nanotube (MWCNT) composite electrodes incorporating platinum black (PtB), palladium black (PdB), or ruthenium black (RuB). The intrinsic electrochemical behaviour of each composite was characterised using outer-sphere redox probes, capacitance measurements, and electrochemical impedance spectroscopy, followed by amperometric assessment of H 2 O 2 and nitrite. PdB-MWCNT electrodes exhibited the highest sensitivity towards H 2 O 2 (0.013 μA μM −1 ; LOD 24 μM), whereas PtB-MWCNT electrodes showed superior performance for nitrite (0.0022 μA μM −1 ; LOD 30 μM), demonstrating analyte-specific electrocatalytic behaviour. SEM-EDX and quantitative image analysis revealed significant differences in catalyst architecture between the composites, indicating that particle distribution, electrochemically accessible surface area, and intrinsic catalytic properties collectively influence performance. Because H 2 O 2 serves as the enzymatically generated signal molecule in first-generation glucose biosensors, the most sensitive H 2 O 2 detecting composite was used as a transducer platform for glucose oxidase-based biosensors. PdB-MWCNT biosensors exhibited higher current responses, faster response times, and stable operation over 30 days. These findings demonstrate how precious-metal identity and catalyst architecture govern analyte-specific sensing behaviour and provide design principles for the development of advanced electrochemical sensors and biosensors.