Fig. 5: Performance contribution and practical application.

a Schematic illustration of the used on-chip micro-cell. Reference electrode: leakless Ag/AgCl. Counter electrode: carbon rod. Electrolyte: N₂ saturated 0.5 M H₂SO₄. b Optical images of Pt-Ti-graphene micro-cell devices with various P_Pt. The thicknesses of Pt and Ti are 10 nm and 2 nm, respectively. c Linear sweep voltammetry (LSV) curves of Pt-Ti-graphene devices in (b), based on the area of exposed Pt (j_Pt). Note that all voltammograms are non-iR corrected. d Top: Scatter plots of j_Pt at −50 mV_vsRHE and −100 mV_vsRHE as a function of P_Pt extracted from statistics based on a minimum of 10 devices. Bottom: Scattered plots of Tafel slope versus P_Pt. The error bars represent the standard deviation. The representative Tafel plots are presented in Supplementary Fig. 46. e–h Proton exchange membrane electrolyzer performance. e Optical images of a typical PEM device with Pt-Ti-carbon paper as the cathode. Anode: IrO₂; Membrane: Nafion 115; Temperature: 80 °C; Electrolyte: H₂O. f Electrochemical impedance spectroscopy (EIS) measurements of PEM devices shown in (e). The red and green curves are for PEM devices with Pt-Ti-carbon paper and Pt-carbon paper as cathode, respectively. Dotted curves and dashed curves are experimental and fitted results, respectively. The inset shows the corresponding equivalent circuit model. Z’ and Z” refer to real and imaginary components of complex impendance, respectivly. R_s, R_{ct_anode}, R_{ct_cathode}, C_{dl_anode}, and C_{dl_cathode} denote solution resistance, charge transfer reisistance of anode and cathode, and double-layer capacitance of anode and cathode, repsectively. The fitting results are presented in Supplementary Tables 2, 3. g Polarization curves during PEM water electrolysis using the Pt-Ti-carbon paper and Pt-carbon paper as cathodes, respectively. h Long-term stability test of the PEM device using the Pt-Ti-carbon paper as cathode under 500 mA cm⁻².