Biomass-derived carbon nanostructures and their applications as electrocatalysts for hydrogen evolution and oxygen reduction/evolution

Biomass derived electrocatalysts with rationally designed activity, selectivity, and stability present a major sustainable approach for the electrochemical production of fuels and value-added chemicals. This review presents recent advances in the field of biomass-derived electrocatalytic nanostructures for the hydrogen evolution reaction (HER) and the oxygen reduction and evolution reactions (oxygen reduction reaction and oxygen evolution reaction), that are subject of major research efforts, as well as public and private investment, as they will play a crucial role in the energy transition and in achieving net zero carbon emissions. The review summarises experimental and theoretical investigations aiming at tuning electrocatalytic performances of sustainable C-based nanostructured materials, and present opportunities for future commercialization of innovative energy materials and applications. In reviewing relevant literature in the field, we focus on the correlation between electrocatalytic activity/selectivity and synthesis methods, composition, physical chemical characteristics, in the attempt to uncover a clear structure-activity relationship. Furthermore, this study provides a critical comparison of the different electrocatalysts in light of their catalytic mechanisms, limiting phenomena, and practical applications for sustainable future technologies

Synthesis of Super-Long Carbon Nanotubes from Cellulosic Biomass under Microwave Radiation

This study reports a novel method for synthesizing super-long carbon nanotubes (SL-CNTs) from cellulose via a microwave treatment process without an external catalyst. CNTs with a length of 0.7–2 mm were obtained via microwave treatment of cellulose biochar temperatures of 1200–1400 °C. Scanning electron microscope (SEM), together with high-resolution transmission electron microscope (HRTEM) results, were used to investigate the changes in the length and morphology of CNTs with respect to treatment temperature. The morphology of CNTs changed from twisted, curved, and threadlike to straight structures. The average length of CNTs after microwave pyrolysis at 600 °C was approximately 600–1800 nm, which after microwave treatment at 1300 °C and 1400 °C increased to about 1–2 mm. X-ray diffractometer (XRD) results confirmed the crystalline structure of CNTs with two prominent peaks at 2θ = 26.3° and 2θ = 43.2° correlating with the graphite (002) and (100) reflections. The ID/IG ratio obtained from Raman spectra of the CNTs decreased to the lowest value of 0.84 after microwave treatment at 1400 °C, implying a high degree of carbon order. The presence of Fe and trace amounts of other elements were confirmed by the energy-dispersive X-ray spectrometer (EDS) and were postulated to have catalyzed the growth of CNTs. The mechanism of the SL-CNTs growth under microwave treatment was proposed and discussed