Double surface modification of graphite felt using a single facile step for electrolytic hydrogen production assisted by urea

Graphite felt (GF) is modified electrochemically using a facile controllable method via scanning the potential from +2 to -1.5 V in solutions containing various NiCl2 concentrations. By increasing the NiCl2 amount, the anodic oxidation and cathodic deposition processes are enhanced, and the GF surface is simultaneously func-tionalized. Firstly, at a high positive potential, GF' functionalization occurs by making a defect in the carbon framework. Then, at a high negative potential, the rate of hydrogen evolution increases and produces a strong homogeneously uniform Ni(OH)2 coating at the GF surface. Modified GF is examined by SEM, mapping EDX, HR-TEM, XPS, XRD, Raman, and contact angle measurements. Interestingly, the Ni(OH)2 film deposited at GF from 100 mM NiCl2 solution (Ni(OH)2/GF-100) enhances the hydrogen evolution reaction in alkaline medium by deriving a current density of 10 mA cm-2 at a low overpotential of 69 mV which approaches the value of the benchmark catalyst. Additionally, the Ni(OH)2/GF-100 electrode supports urea oxidation as it drives a current density of 10 mA cm-2 at a potential of 1.38 V vs RHE. Therefore, Ni(OH)2/GF-100 is used as a bifunctional catalyst to replace the unfavourable anodic reaction (oxygen evolution reaction) with urea oxidation. Further-more, a two electrode cell for urea electrolysis displays a cell voltage of 1.47 V, which is lower than that of water splitting by about 270 mV, to drive a current density of 10 mA cm-2 and shows superb stability over a prolonged electrolysis time of 24 h. So, this approach introduces an energy-saving route.

Automated summary

Graphite felt (GF) is electrochemically modified via a controlled method by scanning the potential from +2 to -1.5 V in solutions with different NiCl2 concentrations. Increasing the NiCl2 amount enhances the anodic oxidation and cathodic deposition processes and functionalizes the GF surface. The modified GF, Ni(OH)2/GF-100, exhibits excellent catalytic activity for hydrogen evolution reaction and urea oxidation. Furthermore, a two-electrode cell for urea electrolysis shows promising energy-saving performance.