Hierarchical Structure of CoMn Nanoparticles Encapsulated in N-Doped Carbon Nanotube Frameworks Grown on Nickel Foam for Water Splitting

Water splitting is an effective approach to produce hydrogen. The direct electrocatalysis of seawater can avoid the use of limited freshwater resources and facilitate large-scale hydrogen production, but stable and efficient electrocatalysts are essential and still challenging. MOF derivatives supported on conductive substrates exhibit promising performances for water splitting. Therefore, we present a two-step approach to construct hierarchical N-doped carbon nanotubes encapsulating Mn₃Co₇ nanoparticles frameworks by pyrolyzing CoMn-MOF grown on nickel foam. In 1.0 M KOH, the catalyst demonstrates remarkable electrocatalytic performance with low overpotentials of 115 and 210 mV for HER and OER, respectively, and achieves a cell voltage of 1.60 V at 10 mA·cm^-2 for overall water splitting. For seawater splitting, it shows promising HER activity with overpotentials of 130 and 306 mV at 10 and 200 mA·cm^-2 in alkaline seawater. More importantly, in natural seawater, the catalyst exhibits excellent stability and attractive HER overpotential of 331 mV at 10 mA·cm^-2, due to regulatory strategies on metal nanoparticles such as CoMn bialloying, space dispersion and charge transport by carbon nanotubes, carbon layers’ encapsulation, and protection. Our work offers a potential approach to synthesizing self-supporting multimetallic nanocarbon materials for seawater splitting and electrochemical energy devices.