Tiny Ni Nanoparticles Embedded in Boron- and Nitrogen-Codoped Porous Carbon Nanowires for High-Efficiency Water Splitting

The integration of nickel (Ni) nanopartide (NP)-embedded carbon layers (Ni@C) into the three-dimensional (3D) hierarchically porous carbon architectures, where ultrahigh boron (B) and nitrogen (N) doping is a potential methodology for boosting Ni catalysts' water splitting performances, was achieved. In this study, the novel 3D ultrafine Ni NP-embedded and B- and N-codoped hierarchically porous carbon nanowires (denoted as Ni@BNPCFs) were successfully synthesized via pyrolysis of the corresponding 3D nickel acetate [Ni(AC)(2)center dot 4H(2)O]-hydroxybenzeneboronic acid-poly- vinylpyrrolidone precursor networks woven by electrospinning. After optimizing the pyrolysis temperatures, various structural and morphological characterization analyses indicate that the optimal Ni@BNPCFs-900 networks own a large surface area, abundant micro/mesopores, and vast carbon edges/defects, which boost doping a large amount of B (5.81 atom %) and N (5.84 atom %) dopants into carbon frameworks with 6.36 atom % of BC3, pyridinic-N (pyridinic-N-Ni), and graphitic-N active sites. Electrochemical measurements demonstrate that Ni@BNPCFs-900 reveals the best hydrogen evolution reaction (HER) and oxygen reduction reaction catalytic activities in an alkaline solution. The HER potential at 10 mA cm(-2) [E-10 = -164.2 mV vs reversible hydrogen electrode (RHE)] of the optimal Ni@BNPCFs-900 is just 96.2 mV more negative than that of the state-of-the-art 20 wt % Pt/C (E-10 = -68 mV vs RHE). In particular, the OER E(10 )and Tafel slope of the optimal Ni@BNPCFs-900 (1.517 V vs RHE and 19.31 mV dec(-1)) are much smaller than those of RuO2 (1.557 V vs RHE and 64.03 mV dec(-1)). For full water splitting, the catalytic current density achieves 10 mA cm(-2) at a low cell voltage of 1.584 V for the (-) Ni@BNPCFs-900 parallel to Ni@BNPCFs-900 (+) electrolysis cell, which is 10 mV smaller than that of the (-) 20 wt % Pt/C parallel to RuO2 (+) benchmark (1.594 V) under the same conditions. The synergistic effects of 3D hierarchically porous structures, advanced charge transport ability, and abundant active centers [such as Ni@BNC, BC3, pyridinic-N (pyridinic-N-Ni), and graphitic-N] are responsible for the excellent water-splitting catalytic activity of the Ni@BNPCFs-900 networks. Especially, because of the remarkable structural and chemical stabilities of 3D hierarchically porous Ni@BNPCFs-900 networks, the (-) Ni@BNPCFs-900 parallel to Ni@ BNPCFs-900 (+) water electrolysis cell displays an excellent stability.

Automated summary

The integration of nickel nanopartide-embedded carbon layers into three-dimensional hierarchically porous carbon architectures, with ultrahigh boron and nitrogen doping, significantly improves the catalytic performance of Ni catalysts for water splitting. The optimized Ni@BNPCFs-900 networks exhibit a large surface area, abundant active sites, and excellent stability, showing superior catalytic activity for hydrogen evolution and oxygen reduction reactions.