Carbon papers (MGL 190, Fuel Cell Earth Co.) were cleaned in a sonication process using acetone (Sigma Aldrich), followed by 2-propanol (Fisher Scientific Co.), and then deionized (DI) water. Subsequently, the surface of carbon papers was treated by air plasma (Harrick Plasma) at a medium intensity of 10.5 W for 1 minute to become hydrophilic. A 0.5 M sodium tungstate (Na2WO4, STREM Co.) solution was prepared by dissolving 1649.3 mg of the salt precursor in 10-mL DI water with the assistance of sonication for 15 minutes (Fig. ). Carbon paper substrates (8mm×20mm) were immersed in the prepared solution for 20 minutes and then dried for 30 minutes at 60 ºC in an oven. To synthesize tungsten carbides, the prepared samples were sandwiched between two pieces of graphite felts, and the temperature was ramped up to 900 ºC by FJH within one second (Fig. and). Tungsten carbides were synthesized for durations of 3, 10, 30, and 60 seconds, corresponding to samples denoted as TC-1, TC-2, TC-3, and TC-4, respectively. Following the fabrication of tungsten carbide on carbon paper substrates, the samples were washed multiple times with ethanol and DI water to remove any salt residues.