Metal Doping Effect of the M–Co₂P/Nitrogen-Doped Carbon Nanotubes (M = Fe, Ni, Cu) Hydrogen Evolution Hybrid Catalysts

Abstract

The enhancement of catalytic performance of cobalt phosphide-based catalysts for the hydrogen evolution reaction (HER) is still challenging. In this work, the doping effect of some transition metal (M = Fe, Ni, Cu) on the electrocatalytic performance of the M-Co2P/NCNTs (NCNTs, nitrogen-doped carbon nanotubes) hybrid catalysts for the HER was studied systematically. The M-Co2P/NCNTs hybrid catalysts were synthesized via a simple in situ thermal decomposition process. A series of techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma-optical emission spectrometry, transmission electron microscopy, and N2 sorption were used to characterize the as-synthesized M-Co2P/NCNTs hybrid catalysts. Electrochemical measurements showed the catalytic performance according to the following order of Fe-Co2P/NCNTs > Ni-Co2P/NCNTs > Cu-Co2P/NCNTs, which can be ascribed to the difference of structure, morphology, and electronic property after doping. The doping of Fe atoms promote the growth of the [111] crystal plane, resulting in a large specific area and exposing more catalytic active sites. Meanwhile, the Fe(δ+) has the highest positive charge among all the M-Co2P/NCNTs hybrid catalysts after doping. All these changes can be used to contribute the highest electrocatalytic activity of the Fe-Co2P/NCNTs hybrid catalyst for HER. Furthermore, an optimal HER electrocatalytic activity was obtained by adjusting the doping ratio of Fe atoms. Our current research indicates that the doping of metal is also an important strategy to improve the electrocatalytic activity for the HER.

Heterostructures for Electrochemical Hydrogen Evolution Reaction: A Review

“…The presence of P decreases the number of Ni sites and hence leads to a moderate binding of H* on the surface, making Ni 2 P an excellent HER catalyst . As expected, hybridizing TMPs with conductive supports is beneficial for increasing active sites and enhancing electrical conductivity, and heteroatom doping may further promote the electrocatalytic performance . Likewise, some TMP/TMP heterostructures are also reported .…”

Non‐Noble Metal‐based Carbon Composites in Hydrogen Evolution Reaction: Fundamentals to Applications

“…The doping effect of Co 2 P on the catalytic activity was investigated in detail. The activity order of the established M‐Co 2 P/NCNTs (M = Fe, Ni, Cu, NCNTs stands for nitrogen‐doped carbon nanotubes) were Fe‐Co 2 P/NCNTs > Ni‐Co 2 P/NCNTs > Cu‐Co 2 P/NCNTs . The activity gaps among the three doped composites are related to the diverse in structure, morphology, and electronic property.…”

Iron‐Doped Cobalt Monophosphide Nanosheet/Carbon Nanotube Hybrids as Active and Stable Electrocatalysts for Water Splitting

“…To further improve the catalytic performance of these phosphides, several approaches such as nanostructuring or hybridization with carbon have been successfully developed . It has been demonstrated that either partially replacing phosphorus (P) atoms with sulfur (S)/selenium (Se) atoms or alloying different metal atoms in the phosphides could further improve their intrinsic activities for electrocatalytic HER compared with the binary single‐phase phosphides . For example, in combination with theoretical calculations and experiments, Jaramillo and co‐workers demonstrated that alloying cobalt (Co) and iron (Fe) in monophosphides could optimize hydrogen adsorption free energy (Δ G H ) on catalysts' surface, and thus improve the intrinsic catalytic activity (based on turnover frequency) of the phosphide alloys for HER .…”