oxygen evolution reaction (OER). However, up to now, the electroactivity of ultrathin nanosheets is still greatly hindered by the poor capacity of cross-plane mass diffusion during electrocatalysis. Alternatively, ultrathin nanomeshes not only perfectly inherit all the merits of ultrathin nanosheets, but more importantly contain well-ordered porous nanostructures. [5] The advanced porous nanostructures of ultrathin nanomeshes could provide abundant channels for allowing rapid mass transport during electrocatalysis. [6] Therefore, crafting ultrathin nanomeshes is an effective way for passing over the hinder of 2D nanosheets and development of high-activity electrocatalysts, however their synthesis remains challenging. At present, most of ultrathin TM-based nanomeshes are prepared by a "hard-template" method, suffering from tedious procedure and harmful acid leaching. Therefore, it is desirable to establish a reliable yet facile method for crafting ultrathin TM-based nanomeshes and uncovering their unique features for electrocatalysis. On the other hand, the increasing environmental pollution and energy crisis caused by the overuse of fossil fuels force us to explore other renewable and green energy for replacing fossil fuels. Hydrogen is a satisfying candidate in virtue of its high efficiency and zero-carbon emission. The generation of hydrogen via water splitting represents a promising way for economical and environment-friendly production of hydrogen. [7] Unfortunately, both two half reactions of water splitting, namely, oxygen evolution reaction at anodic side and hydrogen evolution reaction (HER) at cathodic side, are kinetics adverse reactions, and electrocatalysts are often required for boosting OER and HER to realize preferable efficiency for water splitting. [8] Though noble metal-based electrocatalysts have displayed their incredible performance for OER (i.e., RuO 2 and IrO 2 ) and HER (i.e., Pt/C), the high-cost and low abundance greatly obstruct their following actual application. To this end, it is essential to develop low-cost bifunctional electrocatalysts for both OER and HER, thereby achieving cost-saving and sustainable hydrogen production.Herein, we developed a general route for one-step synthesis of various ultrathin metal borates (i.e., Co-B i , Ni-B i , and Fe-B i ) nanomeshes with well-ordered nanopores. Central to 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, porou...