Hybrid OER Electrocatalyst Combining Mesoporous Hollow Spheres of N, P-Doped Carbon with Ultrafine Co₂NiO_x

A heterostructure combining mesoporous hollow spheres of N, P-doped carbon (meso-NPC) with ultrafine Co2NiOx nanoparticles has been synthesized as a highly active electrocatalyst, named meso-NPC/Co2NiOx. The meso-NPC hollow spheres were first fabricated via a novel nanocasting method using mesoporous SiO2 as the “mold” and the atomic ratio of P in the meso-NPC can be tuned by controlling the amount of one of the filling organics, etidronic acid. Because of the large surface area and abundant surface hydroxyls, the meso-NPC formed strong bonding with the Co2NiOx nanoparticles (<2 nm in size) loaded on it. Serving as an OER electrocatalyst, the heterogeneous meso-NPC/Co2NiOx shows great working enhancement compared to its single-component counterparts. Through further mechanism study by X-ray photoelectron spectroscopy, a strong effect of electron transfer is found from the Co2NiOx to the meso-NPC, which leads to increases in the oxidation state of transition metals (TMs). Most importantly, we also reveal that the increase in the amount of the P dopant in the meso-NPC/Co2NiOx system can efficiently facilitate this metal-to-support charge transfer, which also implies that the biphasic interaction between the Co2NiOx nanoparticles and the meso-NPC hollow spheres generates active catalytic sites of both TM–N–C and TM–P–C surface species.