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

Abstract

The high cost of precursors and the complexity of synthesis procedures have hindered the widespread use of two-dimensional (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.