Microstructure and electrochemical properties for WC/a-C coatings as ECG dry bioelectrodes

WC/a-C composite coatings were deposited using unbalanced magnetron sputtering by adjusting the power of the WC target from 4 kW to 12 kW. The microstructure was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The results indicated the formation of a non-stoichiometric WC_x phase and an a-C phase in the WC/a-C. The WC/a-C coatings demonstrated stable electrochemical performance, characterized by a minimal amplitude of potential drift (0.01 mV) and current drift values ranging from 0.01 nA to 0.03 nA. That was attributed to the presence of amorphous carbon content (C_total/W_W-C: 0.59–1.14) within the coatings. However, the corrosion current densities (I_corr) significantly increased to 1.01×10⁻⁶ A/cm² at higher W content, while the polarization resistance (R_p) decreased to 4.4×10⁴ Ω respectively, indicating a reduction in corrosion resistance with the high WC_x phase. The WC/a-C dry electrodes exhibited stable ECG signals with well-defined PQRST waveforms, closely resembling the electrocardiograms obtained using commercial Ag/AgCl wet electrodes. The T/R ratio for WC/a-C electrodes (0.277–0.30) was found to be comparable to that of Ag/AgCl wet electrodes (0.297). These results demonstrate the suitability of dry WC/a-C electrodes for ECG applications.