1：Experimental Design and Method Selection

BDD films were deposited on Ti substrates with five different pore sizes using hot filament chemical vapor deposition (HFCVD). The influence of the pore size on capacitive properties was assessed.

2：Sample Selection and Data Sources

Five different Ti substrates were chosen, all of them having dimensions of 10 x 10 mm2 but differing porosities - 2.5, 5.0, 20.0, 30.0, 50.0 mm.

3：List of Experimental Equipment and Materials

Seven tungsten filaments with a uniform size of 0.4 mm (diameter) and 180 mm (length) were arranged in an interval of 8 mm. The main deposition parameters of Ti/BDD film were: voltage of 39 V, electric current of 104 A, substrate temperature of 700 °C and gas pressure of 3 KPa, C/H ratio of 1% and B/C ratio of 400 ppm.

4：Experimental Procedures and Operational Workflow

The deposition process comprised two steps: (i) nucleating period of 0.5 h, during which, CH4 acted as the carbon source for nucleation. The deposition parameter for this was: CH4:H2 = 10:1000 (sccm); (ii) growing period of 7.5 h, during which ethanol replaced with CH4 as the carbon source for growing. The deposition parameter was: H2(bubble):B2O3/H2/C2H5OH: H2 = 25: 50:1000 (sccm).

5：Data Analysis Methods

The capacitive characteristics were assessed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). These tests were conducted in a 0.1 M Na2SO4 solution using the CHI660B electrochemical workstation.