Porous Carbon Spheres (PCSs) as a Support for Ni Nanoparticles for Alkaline Water Electrolyzer Cathodes

Porous carbon spheres (PCSs) were synthesized as a support for nickel nanoparticles (Ni NPs) to fabricate a cathode for hydrogen evolution reaction (HER) in an alkaline electrolyte. Characterization of the material revealed that both non-activated and activated PCS exhibited a porous, spherical morphology without pronounced structural confinement, while the deposited Ni NPs showed a tendency to aggregate into large clusters with an average particle size ranging from 16 nm to 22 nm, depending on the type of the PCS used (non-activated vs. activated). X-ray diffraction and Raman spectroscopy confirmed the predominantly amorphous and defect-rich nature of both pristine (PCS) and activated carbon support (PCS-ACT), providing favorable anchoring sites for metal nanoparticles. Although pristine PCS displayed a higher specific surface area than PCS-ACT (284 ± 10 vs. 143 ± 5 m² g^-1, respectively), the surface area of the surface-immobilized Ni NPs was comparable, yielding 5.0 ± 0.3 m² of Ni per gram of the composite. Despite the comparable surface area of the immobilized Ni nanoparticles, electrochemical measurements demonstrated that Ni-PCS outperformed Ni-PCS-ACT in terms of HER electrocatalytic activity. This behavior was attributed to improved accessibility of active Ni sites and reduced pore blockage by evolved hydrogen due to the larger pore diameter of the Ni-PCS material. Thus, these findings suggest that optimizing the pore structure and mass-transport characteristics may be as important as enhancing metal dispersion when designing porous carbon-supported Ni electrocatalysts for alkaline water electrolysis.