Ultrasound-assisted transformation from waste biomass to efficient carbon-based metal-free pH-universal oxygen reduction reaction electrocatalysts

Upcycling biowaste into advanced carbon materials via low-temperature plasma hybrid system: applications, mechanisms, strategies and future prospects

This review focuses on the recent advances in the sustainable conversion of biowaste to valuable carbonaceous materials. This study summarizes the significant progress in biowaste-derived carbon materials (BCMs) via a plasma hybrid system. This includes systematic studies like AI-based multi-coupling systems, promising synthesis strategies from an economic point of view, and their potential applications towards energy, environment, and biomedicine. Plasma modified BCM has a new transition lattice phase and exhibits high resilience, while fabrication and formation mechanisms of BCMs are reviewed in plasma hybrid system. A unique 2D structure can be designed and formulated from the biowaste with fascinating physicochemical properties like high surface area, unique defect sites, and excellent conductivity. The structure of BCMs offers various activated sites for element doping and it shows satisfactory adsorption capability, and dynamic performance in the field of electrochemistry. In recent years, many studies have been reported on the biowaste conversion into valuable materials for various applications. Synthesis methods are an indispensable factor that directly affects the structure and properties of BCMs. Therefore, it is imperative to review the facile synthesis methods and the mechanisms behind the formation of BCMs derived from the low-temperature plasma hybrid system, which is the necessity to obtain BCMs having desirable structure and properties by choosing a suitable synthesis process. Advanced carbon-neutral materials could be widely synthesized as catalysts for application in environmental remediation, energy conversion and storage, and biotechnology.

Noble-metal-free co-N-C catalyst derived from cellulose-based poly(ionic liquid)s for highly efficient oxygen reduction reaction

Noble-Metal-Free nitrogen-doped carbon-based materials are promising electrocatalysts for oxygen reduction reaction (ORR), yet it remains a great challenge to construct efficient porous non-noble metal nitrogen-doped carbon (M-N-C) catalysts with uniform distribution, due to the easy aggregation of metals. Herein, we reported the synthesis and assessment of a novel and efficient noble-metal-free catalyst for oxygen reduction reaction (ORR) from pyrolysis of a cobalt-containing cellulosic poly(ionic liquid) (Co-N-C). The prepared Co-N-C catalyst possesses high surface area, hierarchical porous structure, well-dispersed Co nanoparticles and large amounts of low-coordinated Co active sites. Especially, the Co-N-C-850 sample exhibits a high ORR activity (E_onset = 0.827 V, E_1/2 = 0.74 V) that can rival 20 wt% commercial Pt/C (E_onset = 0.833 V, E_1/2 = 0.71 V) in alkaline media. Moreover, the Co-N-C-850 sample also shows excellent anti-methanol poisoning activity and long-term stability toward ORR compared with commercial Pt/C. Our study provides a promising avenue both for the development of non-noble M-N-C catalysts for fuel cells and functional utilization of cellulose.

Recent Developments in Sonochemical Synthesis of Nanoporous Materials

Ultrasounds are commonly used in medical imaging, solution homogenization, navigation, and ranging, but they are also a great energy source for chemical reactions. Sonochemistry uses ultrasounds and thus realizes one of the basic concepts of green chemistry, i.e., energy savings. Moreover, reduced reaction time, mostly using water as a solvent, and better product yields are among the many factors that make ultrasound-induced reactions greener than those performed under conventional conditions. Sonochemistry has been successfully implemented for the preparation of various materials; this review covers sonochemically synthesized nanoporous materials. For instance, sonochemical-assisted methods afforded ordered mesoporous silicas, spherical mesoporous silicas, periodic mesoporous organosilicas, various metal oxides, biomass-derived activated carbons, carbon nanotubes, diverse metal-organic frameworks, and covalent organic frameworks. Among these materials, highly porous samples have also been prepared, such as garlic peel-derived activated carbon with an apparent specific surface area of 3887 m2/g and MOF-177 with an SSA of 4898 m2/g. Additionally, many of them have been examined for practical usage in gas adsorption, water treatment, catalysis, and energy storage-related applications, yielding satisfactory results.

Ultrasonic synthesis of Mn-Ni-Fe tri-metallic oxide anchored on polymer-grafted conductive carbon for rechargeable zinc-air battery

As a promising electrochemical energy device, a rechargeable zinc-air battery (RZAB) requires cost-effective cathode catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Some earth-abundant transition metal oxides have certain levels of bi-functional ORR/OER catalytic activities yet low electronic conductivities. The addition of high-electronic-conductivity material such as carbon black could result in another problem because there is low compatibility between metal oxide and carbon. In this work, polymer chains are ultrasonically prepared to act as binders to anchor metal-oxide active sites to porous domains of carbon black. The monomer N-isopropyl acrylamide is polymerized under ultrasonication instead of using conventional radical initiators which are dangerous and harmful. Reactive free radicals produced by ultrasonic irradiation can also help to form the Mn-Ni-Fe tri-metallic oxide. Thus, aided by the amide-type polymer as an adhesive, the tri-metallic oxide anchored on polymer-grafted carbon black prepared by ultrasonication possess a large number of metal-oxide active sites and hierarchical pores, contributing substantially to the enhanced ORR/OER electrocatalytic performance in the RZABs. Accordingly, this work provides interesting insight into the effective combination of inherently incompatible components for the fabrication of composite materials from an ultrasonic standpoint.

Heteroatom-doped carbon electrocatalysts prepared from marine biomass cellulose nanocrystals and bio-inspired polydopamine for the oxygen reduction reaction

Heteroatom-doped carbon electrocatalysts were prepared from marine biomass cellulose nanocrystals as potential electrocatalysts for an efficient oxygen reduction reaction.

Boosting electrochemical performance of activated carbon by tuning effective pores and synergistic effects of active species

Clean energy conversion/storage techniques have become increasingly significant because of the increasing energy consumption. Regarding practical applications like zinc-air batteries and supercapacitors, electrode materials are essential and often require both porous networks and active species to enhance their electrochemical performance. Nitrogen-doped porous carbon (NPC) is a kind of promising material, which provides efficient active sites and large surface areas for energy conversion/storage applications. However, rational modulation of properties for maximizing NPC performance is still a challenge. Herein, a promising NPC material derived from natural biomass is successfully synthesized by following a stepwise preparation method. Physisorption and X-ray photoelectron spectroscopy (XPS) analyses demonstrate both pore structures and nitrogen species of the NPC have been delicately tuned. The optimized sample NPC-800-m exhibits excellent performance in both oxygen reduction reaction (ORR) and three-electrode supercapacitor measurement. Moreover, the homemade zinc-air battery and symmetric supercapacitor assembled with NPC-800-m also display outstanding energy and power density as well as durable stability. Density functional theory (DFT) calculations further confirm the synergistic effects among graphitic, pyridinic and pyrrolic nitrogen. The existence of multispecies of nitrogen combined with the optimized pore structure is the key to the high electrochemical performance for NPC-800-m. This work not only provides feasible and green synthetic methodology but also offers original insights into the effective pores and the synergistic effects of different nitrogen species in the NPC materials.

N,S co-doped hierarchical porous carbon from Chinese herbal residues for high-performance supercapacitors and oxygen reduction reaction

The sustainable development of human society is facing challenges of resource depletion, energy crisis and worsening environment. In this work, a typical Chinese herbal residue (gallnut residues), with a large amount of organic waste threatening the environment after extracting the bioactive components, especially in China, was used as a single precursor for both a carbon and heteroatoms source to prepare heteroatoms co-doped hierarchical porous carbon via carbonization and a subsequent KOH activation. The prepared nitrogen, oxygen and sulfur co-doped porous carbons (NOSPC-X) show developed hierarchical micro-mesoporous structures, high specific surface areas, as well as high content of N/S co-doping. When used as supercapacitor electrodes, NOSPC-800 exhibits excellent electrochemical performance with an ultrahigh specific capacitance, a high energy density of 11.25 W h kg-1 at 25 W kg-1 and an excellent charge-discharge cycling stability of 96.5% capacitance remained after 10 000 cycles. As an ORR electrocatalyst, it shows outstanding ORR activity as well as much better stability and methanol-tolerance capacity than that of a commercial Pt/C catalyst. The unique hierarchical micro-mesoporous architecture, high surface area as well as optimal N and S co-doping level make biomass-derived NOSPC-800 an excellent candidate for electrode materials in diverse electrochemical energy applications.