Supercapacitive enhancement using defect-engineered ZnO nanorods anchored on graphene nanowalls hybrid electrodesYang Ma a, b, Stefanos Chaitoglou a, b, Ghulam Farid a, b, Roger Amade a, b, Rogelio Ospina c, Enric Bertran a, ba Department of Applied Physics, University of Barcelona, C/Martí i Franquès, 1, 08028 Barcelona, Catalunya, Spainb ENPHOCAMAT Group, Institute of Nanoscience and Nanotechnology (IN2UB), University of Barcelona, C/Martí i Franquès, 1, 08028 Barcelona, Catalunya, Spainc Escuela de Física, Universidad Industrial de Santander, Carrera 27 calle 9 Ciudad Universitaria Bucaramanga, ColombiaMaterials for Sustainable Development Conference (MATSUS)Proceedings of MATSUS Spring 2024 Conference (MATSUS24)#SUSEN - Advances in Green Energy CarriersBarcelona, Spain, 2024 March 4th - 8thOrganizers: Ungyu Paik and Kangli WangOral, Yang Ma, presentation 115DOI: https://doi.org/10.29363/nanoge.matsus.2024.115Publication date: 18th December 2023Supercapacitors are considered optimal storage devices for electric vehicles and wireless technology due to their superior power density, cycle stability, and charge-discharge efficiency in comparison to traditional batteries [1]. Their inability to act as primary energy sources, however, is hindered by their low energy density. Research efforts are thus concentrated on nanostructured materials that exhibit enhanced specific capacitance, with a focus on carbon-based materials such as activated carbon, carbon nanotubes (CNTs), carbon aerogels and graphene [2]. Supercapacitors operate via electrochemical double-layer capacitors (EDLCs) and pseudocapacitors. EDLCs store energy at the electrode/electrolyte interface through ion adsorption, relying on carbon-based electrodes [3]. Although graphene has superior electrical and thermal conductivity, its theoretical capacitance leads to limitations, despite showing promise. Adjusting the alignment of graphene from horizontal to vertical, as discovered in previous studies, leads to a 38% increase in capacitance, thereby overcoming some of the limitations [4]. Vertical graphene nanowalls (GNWs), manufactured via plasma-enhanced chemical vapor deposition (PECVD), provide superior electrical conductivity and a three-dimensional structure that makes them ideal scaffolds for supercapacitor electrodes [5], [6]. Pseudocapacitors, comprising of metal oxides and polymers, demonstrate a higher specific capacitance in comparison to EDLCs but necessitate a carbon substrate for better charge transfer [7]. The amalgamation of carbon materials and metal oxides manifests a synergistic effect, fulfilling vital requisites for novel energy storage devices. Nevertheless, the elevated cost and toxicity linked with most metal oxides present obstacles. Zinc oxide (ZnO) is a promising electrode material for supercapacitors due to its natural abundance, eco-friendliness, cost-effectiveness, and long cycling life [8]. The specific capacitance of ZnO can be improved by preserving oxygen vacancies, which can be attained by annealing in inert atmospheres [9]. Although integrating ZnO with graphene-based structures has exhibited notable advancements, it remains a complicated and expensive process. In this study, GNWs represent a promising porous structure, offering a substantial surface area for active sites and facilitating rapid ion diffusion. To enhance their specific capacitance, we present a supercapacitive improvement through a hierarchical arrangement of defect-engineered ZnO nanorods (ZNRs) anchored onto the GNWs. This hierarchical structure is synthesized through a multi-step process involving inductively coupled plasma-chemical vapor deposition, magnetron sputtering, and hydrothermal methods. The presence of oxygen vacancy (OV) defects within the ZNRs, induced by argon annealing, has been characterized utilizing X-ray photoelectron spectroscopy. The emergence of OV defects below the conduction band of the ZNRs results in a narrowing of the bandgap within the hybrid structure, thereby enhancing its conductivity and increasing the reaction sites. In the capacity of supercapacitor electrodes, the ZNRs/GNWs hybrids were evaluated in an aqueous KOH electrolyte solution, operating within a voltage range of 0.5 V and at a current density of 0.1 mA cm-2. This assessment yielded an area capacitance of 21.45 mF cm-2, signifying a 1.5-fold increase in capacitance compared to GNWs grown on graphite sheets. The ZNRs/GNWs hybrid demonstrates remarkable electrochemical performance and exhibits substantial potential for energy storage applications. Our work is expected to offer valuable insights for the enhancement of electrochemical properties in various composite and hybrid materials. References:[1] Lethien, C.; Le Bideau, J.; Brousse, T. Challenges and Prospects of 3D Micro-Supercapacitors for Powering the Internet of Things. Energy Environ. Sci. 2019, 12, 96-115.[2] Zhang, Y.; Sun, X.; Pan, L.; Li, H.; Sun, Z.; Sun, C.; Tay, B. K. Carbon Nanotube–ZnO Nanocomposite Electrodes for Supercapacitors. Solid State Ionics. 2009, 180, 1525-1528.[3] Wen, S.; Jung, M.; Joo, O.-S.; Mho, S.-i. EDLC Characteristics with High Specific Capacitance of the CNT Electrodes Grown on Nanoporous Alumina Templates. Curr. Appl Phys. 2006, 6, 1012-1015.[4] Zhang, Y.; Zou, Q.; Hsu, H. S.; Raina, S.; Xu, Y.; Kang, J. B.; Chen, J.; Deng, S.; Xu, N.; Kang, W. P. Morphology Effect of Vertical Graphene on the High Performance of Supercapacitor Electrode. ACS Appl. Mater. Interfaces. 2016, 8, 7363-7369.[5] Yen, H.-F.; Horng, Y.-Y.; Hu, M.-S.; Yang, W.-H.; Wen, J.-R.; Ganguly, A.; Tai, Y.; Chen, K.-H.; Chen, L.-C. Vertically Aligned Epitaxial Graphene Nanowalls with Dominated Nitrogen Doping for Superior Supercapacitors. Carbon. 2015, 82, 124-134.[6] Chi, Y.-W.; Hu, C.-C.; Shen, H.-H.; Huang, K.-P. New Approach for High-Voltage Electrical Double-Layer Capacitors Using Vertical Graphene Nanowalls with and without Nitrogen Doping. Nano Lett. 2016, 16, 5719-5727.[7] Zhou, Y. K.; He, B. L.; Zhang, F. B.; Li, H. L. Hydrous Manganese Oxide/Carbon Nanotube Composite Electrodes for Electrochemical Capacitors. J. Solid State Electrochem. 2004, 8, 482-487.[8] Zhou, X.; Ma, L. MnO2/ZnO Porous Film: Electrochemical Synthesis and Enhanced Supercapacitor Performances. Thin Solid Films. 2015, 597, 44-49.[9] Dillip, G. R.; Banerjee, A. N.; Anitha, V. C.; Deva Prasad Raju, B.; Joo, S. W.; Min, B. K. Oxygen Vacancy-Induced Structural, Optical, and Enhanced Supercapacitive Performance of Zinc Oxide Anchored Graphitic Carbon Nanofiber Hybrid Electrodes. ACS Appl. Mater. Interfaces. 2016, 8, 5025-5039.Acknowledgements:This publication of this work is funded by Grant PID2020-116612RB-C32 provided by MCIN/AEI/ 10.13039/501100011033, in conjunction with financial support from the "European Union NextGenerationEU/PRTR". The authors acknowledge financial support from projects PID2020-116612RB-C32, PDC2021-121868-C22, TED2021-132070B-C21, TED2021-131442B-C33 funded by MCIN/AEI/10.13039/501100011033 and, as appropriate, by "ERDF A way of making Europe", and by the "European Union Next Generation EU/PRTR". The ENPHOCAMAT group acknowledges support from the AGAUR of Generalitat de Catalunya, Project No. 2021SGR00936. Y. M. acknowledges the support from the predoctoral fellowship program funded by the China Scholarship Council affiliated with the Ministry of Education of the P. R China. S. C. acknowledges support from the postdoctoral fellowship programme Beatriu de Pinós, funded by the Secretary of Universities and Research (Government of Catalonia) through grant agreement 801370 (H2020-MSCA-COFUND-2017) and from the MSCA fellowship funded by the European Commission through grant agreement 101062014 (HORIZON Europe-MSCA-2021-PF-01). R. O. acknowledges the financial support from the Requalification of the Spanish University System 2021-23 program funded by the Next Generation EU program through the Ministry of Universities of Spanish Government. G. F. acknowledges the support from the PRE-DOCSUB (APIF) funded by the MICINN of Spanish Government. © FUNDACIO DE LA COMUNITAT VALENCIANA SCITOnanoGe is a prestigious brand of successful science conferences that are developed along the year in different areas of the world since 2009. 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