General Synthesis of Ultrathin Metal Borate Nanomeshes Enabled by 3D Bark‐Like N‐Doped Carbon for Electrocatalysis

Ultrathin nanomeshes perfectly inherit the integrated advantages of ultrathin 2D materials and porous nanostructures, which have shown their great application potential in catalysis and electronic devices. Here, the general synthesis of ultrathin metal borate (i.e., Co‐B_i, Ni‐B_i, and Fe‐B_i) nanomeshes is reported by capitalizing on 3D bark‐like N‐doped carbon (denoted BNC) as nanoreactors. Indeed, this strategy is straightforward, only comprising a one‐step reaction between metal cations and sodium borohydride without using templates. As nanoreactors, the BNC derived from biomass waste of lychee exocarp possesses distinctive advantages of low cost, fractured textures, porous nanostructures (surface area: 1915.5 m² g^?1), electronegative surface (zeta potential: ?43.4 mV), and superhydrophilicity for greatly facilitating the adsorption of metal cations with strong strength to effectively control the growth of 2D nanomeshes. The as‐synthesized Co‐B_i and Ru‐doped Co‐B_i (Ru‐Co‐B_i) nanomeshes exhibit excellent performance for the oxygen evolution reaction and hydrogen evolution reaction, respectively. Impressively, the water splitting device based on the Co‐B_i and Ru‐Co‐B_i nanomeshes can enable a current density of 10 mA cm^?2 at a small cell voltage of 1.53 V. Therefore, this work paves new avenues for the facile synthesis of ultrathin metal nanomeshes.