High-density defect-induced ultrahigh boron and nitrogen doping of iron-copper-functionalized porous carbon nanosheets for enhanced water splitting

The high cost of precursors and the complexity of synthesis procedures have hindered the widespread use of twodimensional (2D) porous carbon nanosheets in water splitting. In this study, we successfully developed a low-cost method for the rapid synthesis of three-dimensional (3D) hierarchically porous architectures self-assembled from iron-copper nanoparticles embedded in boron (B)/nitrogen (N)-codoped 2D porous carbon nanosheets (denoted as FeCu@BNPCNS). The optimal FeCu@BNPCNS-900 nanosheet exhibited a large surface area, abundant porous channels, meso/macropores, and carbon edges/defects. Particularly, 10.25 atom% of B/N electrochemically active centers (such as pyridinic-N (including the metal-nitrogen-carbon species), pyrrolic-N, graphitic-N, and BC3) were successfully doped into the optimal FeCu@BNPCNS-900 nanosheets. In an alkaline solution, FeCu@BNPCNS-900 exhibited excellent electrocatalytic activity for hydrogen evolution reaction (HER), which was higher than that of the commercial 20 wt% Pt/C. For example, the HER potential of FeCu@BNPCNS-900 at 10 mA cm-2 [E10; -202.3 mV vs. reversible hydrogen electrode (RHE)] was only 140.2 mV more negative than that of 20 wt% Pt/C (-62.1 mV vs. RHE). Additionally, FeCu@BNPCNS-900 exhibited a slightly lower oxygen evolution reaction (OER) electrocatalytic activity than the ruthenium oxide (RuO2). Particularly, the OER E10 potential (+1.634 V vs. RHE) of FeCu@BNPCNS-900 was only 76 mV more positive than that of RuO2 (+1.558 V vs. RHE). The FeCu@BNPCNS-900||FeCu@BNPCNS-900 cell achieved 10 mA cm-2 at 1.613 V, which was 58 mV more negative than that of the 20 wt% Pt/C||RuO2 cell (1.671 V). The excellent water-splitting performance of FeCu@BNPCNS-900 could be attributed to the 3D hierarchically porous architecture, abundant channels/mesopores, and uniformly dispersed electrocatalytically active sites. Therefore, we developed an efficient strategy for the large-scale and low-cost synthesis of 2D porous carbon nanosheets without the need for precursors, templates, or surfactants.