Research Article pubs.acs.org/journal/ascecg
Sustainable Route for Molecularly Thin Cellulose Nanoribbons and Derived Nitrogen-Doped Carbon Electrocatalysts Yun Lu,*,†,§ Guichao Ye,†,‡ Xilin She,‡ Siqun Wang,†,∥ Dongjiang Yang,*,‡,⊥,# and Yafang Yin*,† †
Department of Wood Anatomy and Utilization, Research Institute of Wood Industry, Chinese Academy of Forestry, Yard 1, Dongxiaofu, Xiangshan Road, Haidian District, Beijing 100091, People’s Republic of China ‡ Collaborative Innovation Center for Marine Biomass Fibers, Materials and Textiles of Shandong Province, School of Environmental Science and Engineering, Qingdao University, 308 Ningxia Road, Qingdao 266071, People’s Republic of China § Key Laboratory of Bio-Based Material Science and Technology Ministry of Education, Northeast Forestry University, 26 Hexing Road, Harbin 150040, People’s Republic of China ∥ Center for Renewable Carbon, University of Tennessee, 527 Andy Holt Tower, Knoxville, Tennessee 37996, United States ⊥ Queensland Micro- and Nanotechnology Centre (QMNC), Nathan Campus Griffith University, 170 Kessels Road, Brisbane, Queensland 4111, Australia # Key Laboratory of Coal Science and Technology, Taiyuan University of Technology, Ministry of Education and Shanxi Province, No. 79 West Yingze Avenue, Wanbailin District, Taiyuan 030024, China S Supporting Information *
ABSTRACT: Ultrathin cellulose nanoribbons were extracted from earth-abundant biomass using 2,2,6,6-tetramethylpiperidine-1-oxylcatalyzed (TEMPO-catalyzed) oxidation and sonication processes. By two TEMPO-oxide systems with different processing times, TEM and AFM observations indicate the obtained cellulose nanoribbons (Cel-NRs) with dimensions of 400−800 nm in length, 1.72−2.54 nm in width, and 0.78−2.67 nm in thickness. The dimension data indicate that the Cel-NRs from the TEMPO/NaBr/NaClO system are much shorter but contain more cellulose chains than those from the TEMPO/NaClO/NaClO2 system. Moreover, these abundant biomass nanoribbons were fabricated from direct pyrolysis with NH3 activation. The obtained highly active nitrogen-doped carbon nanoribbons (N-CNRs) and metal-free oxygen reduction reaction (ORR) electrocatalysts show superb ORR activity (half-wave potential of 0.71 and 0.73 V versus reversible hydrogen electrode) and high selectivity (electron-transfer number of 3.26 and 3.74 at 0.8 V), comparable current density and onset potential (0.906 and 0.926 V), excellent electrochemical stability (higher than 89.5% and 91.6% after 20 000 potential cycles) in alkaline media, and better resistance to crossover effects in the ORR. More importantly, when used as a cathode catalyst for constructing the air electrode of the Zn−air battery, the N-CNRs exhibit super long-term stability and a capacity of 587 and 583 mAh g−1 at the discharge current densities of 5 and 20 mA cm−2, respectively, which are highly comparable with those of the state-of-the-art Pt/ C catalyst (20 wt % Pt, Hispec 3000). This indicates that our present work is the first example of using atomically thin carbon nanoribbons as the metal-free electrocatalyst substitution to Pt for developing high-performance metal−air batteries from earthabundant terrestrial plants. KEYWORDS: Cellulose, TEMPO, Nanoribbons, Oxygen reduction, Zn−air battery
■
after being carbonized,8 are ideal substrates for catalysis, surface chemistry, and electrochemistry with a large surface area; they also have well-controlled surface sites, high mechanical strength, low density, and excellent quantum size effect. Therefore, to exfoliate cellulose into ultrathin elementary fibril fractions with dramatically decreased lateral dimensions is an ideal sustainable strategy to fabricate ultrathin carbon nano-
INTRODUCTION Nanofibrillated cellulose (NFC), well-known as a 1D nanofiber with a 20−80 nm diameter, has been successively extracted from various plants1,2 and has an outstanding performance with the combination of several qualities, high specific strength, stiffness, renewable resource, and low-cost, over different nonrenewable energy resources.3−5 As an inexhaustible natural resource, the ultrathin NFC (diameter
