Novel N-Mo2 C Active Sites for Efficient Solar-to-Hydrogen Generation

Rational design of pyrrolic-N dominated carbon material derived from aminated lignin for Zn-ion supercapacitors

Developing highly efficient, sustainable carbon cathodes is essential for emerging Zn-ion hybrid supercapacitors (ZICs). Herein, lignin's novel chemical modification (amination) has been developed to produce high quantity pyrrolic-N moieties as active sites. Furthermore, chemically modified amine moieties in lignin are vital as a natural self-activating template to generate hierarchical porosity in the 2D (graphene-like) architecture with exceedingly high surface area (2926.4 m²g^-1). The rationally introduced dominated pyrrolic-N moieties boost the Zn-ion storage capacity and reaction kinetics due to the dual energy storage mechanism and efficient charge transfer between pyrrolic-N and Zn⁺² ions. Furthermore, the pyrrolic-N species are energetically favorable for the adsorption of Zn⁺² ions by the formation of N-Zn⁺² chemical bonds. Besides, the nitrogen oxides reduce the intrinsic resistance and induce a more polarized surface, resulting in high wettability and efficient transfer of electrolytes into the pores of hydrophobic carbon materials. Subsequently, the chemically modified lignin-derived activated carbon material (Chem-ACM) as a cathode in ZICs delivers a high capacity of 161.2 mA h g^-1 at 1 A g^-1 with the admirable energy density of 106.7 W h kg^-1 at 897 W kg^-1 and excellent retention capacity (94%) after 10,000 cycles. Mainly, the assembled quasi solid-state ZICs using Chem-ACM retains the remarkable storage capacity (202 mA h g^-1 at 0.2 Ag^-1) even at a high bending angle. Notably, the Chem-ACM has been further employed in symmetric supercapacitors as an electrode, and it displays exceptional specific capacitance of 354 Fg^-1 at 0.5 Ag^-1 with tremendous energy (43.5 W h kg^-1) and the power density (0.53 kW kg^-1). Additionally, the charge storage capability of Chem-ACM is positively dependent on high nitrogen contents, and it is extrapolated that pyrrolic-N moieties are dominant active sites. Hence, the designed amination-assisted biocarbon synthesis provides a new way to prepare high nitrogen-containing biocarbon for ZICs and further understand pyrrolic-N species' impact on Zn-ion storage.

Chemically modified self-doped biocarbon via novel sulfonation assisted sacrificial template method for high performance flexible all solid-state supercapacitor

The development of lignin-based carbon electrodes for high-performance flexible, solid-state supercapacitors in next-generation soft and portable electronics, has received much attention. Herein, a self-doped multi-porous lignin-based biocarbon (SUMBC) has been prepared via a simple sulfonation assisted sacrificial template method for the effective formation of oxygenated C-S-C moieties in the carbon network. In this proposed method, the sulfonate moieties in lignin are responsible for the successful decoration of oxygen enriched C-S-C moieties as well as for creating the optimal multilevel porous architecture (ultra-micropores, micropores and mesopores) in the carbon matrix with a large surface area (3149 m² g^-1). Because the sulfonate functionalities yield more sulfur species and induce further defects into carbon framework, in the activation process, these sulfur functionalities produce additional narrow micropores. Benefiting from the above unique feature, the supercapacitor (SC) with the SUMBC electrode delivers excellent capacitive behavior in both acidic (2 M H₂SO₄) and alkaline (6 M KOH) liquid electrolytes. More prominently, the all-solid state, symmetric supercapacitors assembled by SUMBC show outstanding capacitance of ~140 F g^-1 at 0.5 A g^-1 in two different devices and reveals high energy density (~5.41 W h kg^-1 at 0.5 k W kg^-1 power density) and excellent stability. In addition, the solid-state supercapacitors manifest a remarkable flexibility at different bending angles. Hence, the present work provides a new strategy for the preparation of efficient biocarbons via a facile sulfonation assisted sacrificial template method; moreover, the high-performance all-solid supercapacitors based on sulfonated modified lignin has great potential in the field of portable and wearable energy storage devices.