@article{he_zhang_song_zhao_gao_2024, title={Modeling of yarn-shaped supercapacitors - Unraveling its length dependent output}, volume={595}, ISSN={["1873-2755"]}, DOI={10.1016/j.jpowsour.2024.234067}, abstractNote={Yarn-shaped energy-storage devices are promising power sources for electronic textiles, since they carry the possibility to be seamlessly integrated into various fabrics. The energy/power outputs of these devices are inevitably a function of their lengths, the dependence on which is yet to be thoroughly explored. Despite numerous research on yarn-shaped supercapacitors (YSCs) and batteries, the correlation between yarn length and their electrochemical output remains ambiguous, and sometimes even controversial. Herein, a dual transmission-line model for YSCs is created and used to fit the electrochemical impedance spectra (EIS) of YSCs ranging from 10 cm to 300 cm in length. The evolution of equivalent series resistances, electrolyte diffusion resistances and capacitances of YSCs as yarn length increases is investigated. Given the structure and components of YSCs used in this study, a favorable length range of 40–60 cm has been identified to achieve the best electrochemical performance, including the lowest internal resistance and the highest specific capacitance, where the highest energy and power densities sit. The mathematical model introduced in this work provides a reasonable description of the electrochemical behaviors of YSCs in different yarn lengths, offering a theoretical foundation to guide the design of these devices for specific application scenarios.}, journal={JOURNAL OF POWER SOURCES}, author={He, Nanfei and Zhang, Xi and Song, Junhua and Zhao, Feng and Gao, Wei}, year={2024}, month={Mar} }
 @article{he_king_xie_zhao_gao_2023, title={A Multidirectional Forearm Electromagnetic Generator Designed via Numerical Simulations}, volume={12}, ISSN={["2076-0825"]}, DOI={10.3390/act12060225}, abstractNote={Harvesting biomechanical energy from daily human body motions provides a promising and sustainable power solution for wearable electronics, whose current power supplies, i.e., batteries, have unsatisfactory capacity and durability due to volume, shape, and flexibility constraints. Electromagnetic generators (EMGs) are favorable energy transducers because of their high energy-conversion efficiency, low dependence on frequencies, and long-term stability. However, an EMG that can effectively harvest energy from multi-directional arm motions at aperiodic low frequencies are yet to be created. Here, we introduce a unique EMG configuration by combining a linear and a helix frame into a monolithic unit (EMG-LH), enabling the EMG to scavenge energy from all kinds of arm motions up to 6 degrees of freedom (DOFs) (movement along XYZ axes and forearm rotations). The EMG frame geometry is designed and optimized according to numerical simulations. To clarify the working mechanism and maximize the power output, the copper coils’ winding pattern, the magnets’ velocity profiles, and the resulting voltage output are numerically simulated and then experimentally verified. Our EMG-LH outperforms linear EMGs (EMG-Ls) and helix EMGs (EMG-Hs) in harvesting energy from all arm motions. This work explicitly presents a forearm-wearable energy harvester as a sustainable power source for wearable electronics.}, number={6}, journal={ACTUATORS}, author={He, Nanfei and King, Colton and Xie, Qizheng and Zhao, Feng and Gao, Wei}, year={2023}, month={Jun} }
 @article{subjalearndee_he_cheng_tesatchabut_eiamlamai_phothiphiphit_saensuk_limthongkul_intasanta_gao_et al._2023, title={Wet Spinning of Graphene Oxide Fibers with Different MnO2 Additives}, volume={15}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.3c02989}, abstractNote={We present the fabrication of graphene oxide (GO) and manganese dioxide (MnO2) composite fibers via wet spinning processes, which entails the effects of MnO2 micromorphology and mass loading on the extrudability of GO/MnO2 spinning dope and on the properties of resulted composite fibers. Various sizes of rod and sea-urchin shaped MnO2 microparticles have been synthesized via hydrothermal reactions with different oxidants and hydrothermal conditions. Both the microparticle morphology and mass loading significantly affect the extrudability of the GO/MnO2 mixture. In addition, the orientation of MnO2 microparticles within the fibers is largely affected by their microscopic surface areas. The composite fibers have been made electrically conductive via chemical or thermal treatments and then applied as fiber cathodes in Zn-ion battery prototypes. Thermal annealing under an argon atmosphere turns out to be an appropriate method to avoid MnO2 dissolution and leaching, which have been observed in the chemical treatments. These rGO/MnO2 fiber cathodes have been assembled into prototype Zn-ion batteries with Zn wire as the anode and xanthan-gum gel containing ZnSO4 and MnSO4 salts as the electrolyte. The resulted electrochemical output depends on the annealing temperature and MnO2 distribution within the fiber cathodes, while the best performer shows stable cycling stability at a maximum capacity of ca. 80 mA h/g.}, number={15}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Subjalearndee, Nakarin and He, Nanfei and Cheng, Hui and Tesatchabut, Panpanat and Eiamlamai, Priew and Phothiphiphit, Somruthai and Saensuk, Orapan and Limthongkul, Pimpa and Intasanta, Varol and Gao, Wei and et al.}, year={2023}, month={Apr}, pages={19514–19526} }
 @article{mainka_gao_he_dillet_lottin_2022, title={A General Equivalent Electrical Circuit Model for the characterization of MXene/graphene oxide hybrid-fiber supercapacitors by electrochemical impedance spectroscopy - Impact of fiber length}, volume={404}, ISSN={["1873-3859"]}, DOI={10.1016/j.electacta.2021.139740}, abstractNote={Performance engineering of electrochemical energy-storage devices such as Supercapacitors (SCs) requires updated modeling capable of characterizing their electrical output in unique device geometries. In this work, an Equivalent Electrical Circuit (EEC) is developed to fit the impedance data of pseudo-capacitive and electrostatic fiber-shaped supercapacitors (FSCs). The model is applied for the interpretation of impedance data measured on FSCs made of reduced Graphene Oxide (rGO) and MXene in the case of pseudo-capacitors and pure carbon in the case of Electrical Double-Layer Capacitors (EDLCs) as active electrode materials, and polyvinylalcohol (PVA) gel infiltrated with sulfuric acid as the electrolyte and separator. The FSC charge storage behavior is modeled using a Transmission Line Model (TLM) including a finite Warburg impedance for pseudo-capacitance, and a Constant-Phase Element (CPE) for the electrostatic contribution. The high frequency part of the Nyquist plots is characterized by a 45° straight line and the use of a TLM clearly improves the fit quality compared to a Randles circuit usually used for pseudo-capacitor modeling. The difference between the two ciruits becomes more visible as the length of the SC yarns increases, which is consistent with the observed increase in internal resistance with fiber length evidenced with the TLM. Furthermore, the fitting results indicate that the internal resistance of the TLM predominantly corresponds to the electrical resistance of the fiber, i.e. the electron conductive phase of the electrode, instead of the electrolyte ionic resistance in usual SCs. Finally, the low frequency part of the spectra is correctly modeled by a CPE without any leakage resistance, showing that self-discharge is not a significant issue for the electrostatic contribution, at least in the frequency range tested.}, journal={ELECTROCHIMICA ACTA}, author={Mainka, Julia and Gao, Wei and He, Nanfei and Dillet, Jerome and Lottin, Olivier}, year={2022}, month={Feb} }
 @article{subjalearndee_he_cheng_tesatchabut_eiamlamai_limthongkul_intasanta_gao_zhang_2022, title={Gamma((sic))-MnO2/rGO Fibered Cathode Fabrication from Wet Spinning and Dip Coating Techniques for Cable-Shaped Zn-Ion Batteries}, volume={1}, ISSN={["2524-793X"]}, url={https://doi.org/10.1007/s42765-021-00118-3}, DOI={10.1007/s42765-021-00118-3}, journal={ADVANCED FIBER MATERIALS}, author={Subjalearndee, Nakarin and He, Nanfei and Cheng, Hui and Tesatchabut, Panpanat and Eiamlamai, Priew and Limthongkul, Pimpa and Intasanta, Varol and Gao, Wei and Zhang, Xiangwu}, year={2022}, month={Jan} }
 @article{ramesh_davis_roros_zhou_he_gao_menegatti_khan_genzer_2022, title={Nonwoven Membranes with Infrared Light-Controlled Permeability}, volume={9}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.2c13280}, abstractNote={This study presents the development of the first composite nonwoven fiber mats (NWFs) with infrared light-controlled permeability. The membranes were prepared by coating polypropylene NWFs with a photothermal layer of poly(N-isopropylacrylamide) (PNIPAm)-based microgels impregnated with graphene oxide nanoparticles (GONPs). This design enables "photothermal smart-gating" using light dosage as remote control of the membrane's permeability to electrolytes. Upon exposure to infrared light, the GONPs trigger a rapid local increase in temperature, which contracts the PNIPAm-based microgels lodged in the pore space of the NWFs. The contraction of the microgels can be reverted by cooling from the surrounding aqueous environment. The efficient conversion of infrared light into localized heat by GONPs coupled with the phase transition of the microgels above the lower critical solution temperature (LCST) of PNIPAm provide effective control over the effective porosity, and thus the permeability, of the membrane. The material design parameters, namely the monomer composition of the microgels and the GONP-to-microgel ratio, enable tuning the permeability shift in response to IR light; control NWFs coated with GONP-free microgels displayed thermal responsiveness only, whereas native NWFs showed no smart-gating behavior at all. This technology shows potential toward processing temperature-sensitive bioactive ingredients or remote-controlled bioreactors.}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Ramesh, Srivatsan and Davis, Jack and Roros, Alexandra and Zhou, Chuanzhen and He, Nanfei and Gao, Wei and Menegatti, Stefano and Khan, Saad and Genzer, Jan}, year={2022}, month={Sep} }
 @article{he_song_liao_zhao_gao_2022, title={Separator threads in yarn-shaped supercapacitors to avoid short-circuiting upon length}, volume={6}, ISSN={["2397-4621"]}, DOI={10.1038/s41528-022-00150-2}, abstractNote={Abstract Yarn-shaped supercapacitors (YSCs) are becoming promising energy-supply units with decent mechanical flexibility to be integrated into e-textiles in various shapes and locations. However, a robust YSC configuration that can provide long-term and reliable power output, especially after rigorous weaving and knitting processes, as well as all kinds of end uses, is yet to be established. Most YSCs today still suffer from short-circuiting upon length, primarily due to the structure failure of gel electrolyte that also works as the separator. Herein, we report the incorporation of separator threads in a twisted YSC, to withstand repetitive mechanical deformations. Separator threads are wrapped outside of yarn electrodes as a scaffold to accommodate gel electrolyte, while chemistry and wrapping density of these threads are investigated. With processing parameters optimized, we present an YSC configuration that can bear mechanical deformations along almost all directions, leading to reliable power units in woven or knit fabrics.}, number={1}, journal={NPJ FLEXIBLE ELECTRONICS}, author={He, Nanfei and Song, Junhua and Liao, Jinyun and Zhao, Feng and Gao, Wei}, year={2022}, month={Mar} }
 @article{wang_shim_he_pourdeyhimi_gao_2021, title={Modeling the Triboelectric Behaviors of Elastomeric Nonwoven Fabrics}, volume={11}, ISSN={["1521-4095"]}, url={https://doi.org/10.1002/adma.202106429}, DOI={10.1002/adma.202106429}, abstractNote={Theoretical modeling of triboelectric nanogenerators (TENGs) is fundamental to their performance optimization, since it can provide useful guidance on the material selection, structure design, and parameter control of relevant systems. Built on the theoretical model of film‐based TENGs, here, an analytical model is introduced for conductor‐to‐dielectric contact‐mode nonwoven‐based TENGs, which copes with the unique hierarchical structure of nonwovens and details the correlation between the triboelectric output (maximum transferred charge density) and nonwoven structural parameters (thickness, solidity, and average fiber diameter). A series of styrene–ethylene–butylene–styrene nonwoven samples are fabricated through a melt‐blowing process to map nonwoven structural features within certain ranges, while an ion‐injection protocol is adopted to quantify the triboelectric output with superior consistency and reproducibility. With a database containing structural features and triboelectric output of 43 nonwoven samples, a good model fitting is achieved via nonlinear regression analysis in Python, which also shows good predictive power and suggests the existing of tribo‐output maxima at a specific thickness, solidity, or average fiber diameter when other structural parameters are fixed. The model is also successfully applied to a group of polypropylene meltblown nonwovens, which verifies its universality on meltblown‐nonwoven‐based TENGs.}, journal={ADVANCED MATERIALS}, publisher={Wiley}, author={Wang, Yanan and Shim, Eunkyoung and He, Nanfei and Pourdeyhimi, Behnam and Gao, Wei}, year={2021}, month={Nov} }
 @article{he_liao_zhao_gao_2020, title={Dual-Core Supercapacitor Yarns: An Enhanced Performance Consistency and Linear Power Density}, volume={12}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.0c00182}, abstractNote={Pliable energy-storage devices are arousing great attention recently due to their important roles in rapid-growing wearable/implantable electronic systems, among which yarn-shaped supercapacitors (YSCs) are promising candidates since they carry great design versatility with tunable sizes and shapes. However, existing challenges of YSCs include inferior power output and poor performance consistency as compared to their planner counterparts, mainly due to their unique linear geometry and curved interfaces. Here an YSC comprised of wet-spun fibers of reduced graphene oxide (rGO) and MXene sheets is demonstrated, which exhibits prominent decreases in equivalent series resistance (ESR), and thus increases in power output upon increasing length, which is contradictory to the common expectations of a typical YSC, carrying revolutionary promises for practical applications. A much higher power density (2502.6 μW cm-2) can be achieved at an average energy density of 27.1μWh cm-2 (linearly, 510.9 μW cm-1 at 5.5 μWh cm-1) via our unique dual-core design. The YSCs also present good stability upon stretching and bending, compatible with further textile processing. This work provides new insights toward the fabrication of textile-based energy-storage devices for real-world applications.}, number={13}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={He, Nanfei and Liao, Jinyun and Zhao, Feng and Gao, Wei}, year={2020}, month={Apr}, pages={15211–15219} }
 @article{he_patil_qu_liao_zhao_gao_2020, title={Effects of Electrolyte Mediation and MXene Size in Fiber-Shaped Supercapacitors}, volume={3}, ISSN={["2574-0962"]}, DOI={10.1021/acsaem.0c00024}, abstractNote={Flexible and pliable fiber electrodes with decent electrical conductivity and high capacitance density are crucial to fiber-shaped supercapacitors (FSCs) whose real-world applications include elect...}, number={3}, journal={ACS APPLIED ENERGY MATERIALS}, author={He, Nanfei and Patil, Shradha and Qu, Jiangang and Liao, Jinyun and Zhao, Feng and Gao, Wei}, year={2020}, month={Mar}, pages={2949–2958} }
 @article{schneible_shi_young_ramesh_he_dowdey_dubnansky_libya_gao_santiso_et al._2020, title={Modified gaphene oxide (GO) particles in peptide hydrogels: a hybrid system enabling scheduled delivery of synergistic combinations of chemotherapeutics}, volume={8}, ISSN={["2050-7518"]}, DOI={10.1039/d0tb00064g}, abstractNote={The scheduled delivery of synergistic drug combinations is increasingly recognized as highly effective against advanced solid tumors. Of particular interest are composite systems that release a sequence of drugs with defined kinetics and molar ratios to enhance therapeutic effect, while minimizing the dose to patients. In this work, we developed a homogeneous composite comprising modified graphene oxide (GO) nanoparticles embedded in a Max8 peptide hydrogel, which provides controlled kinetics and molar ratios of release of doxorubicin (DOX) and gemcitabine (GEM). First, modified GO nanoparticles (tGO) were designed to afford high DOX loading and sustained release (18.9% over 72 h and 31.4% over 4 weeks). Molecular dynamics simulations were utilized to model the mechanism of DOX loading as a function of surface modification. In parallel, a Max8 hydrogel was developed to release GEM with faster kinetics and achieve a 10-fold molar ratio to DOX. The selected DOX/tGO nanoparticles were suspended in a GEM/Max8 hydrogel matrix, and the resulting composite was tested against a triple negative breast cancer cell line, MDA-MB-231. Notably, the composite formulation afforded a combination index of 0.093 ± 0.001, indicating a much stronger synergism compared to the DOX-GEM combination co-administered in solution (CI = 0.396 ± 0.034).}, number={17}, journal={JOURNAL OF MATERIALS CHEMISTRY B}, author={Schneible, John D. and Shi, Kaihang and Young, Ashlyn T. and Ramesh, Srivatsan and He, Nanfei and Dowdey, Clay E. and Dubnansky, Jean Marie and Libya, Radina L. and Gao, Wei and Santiso, Erik and et al.}, year={2020}, month={May}, pages={3852–3868} }
 @article{he_shan_wang_pan_qu_wang_gao_2019, title={Mordant inspired wet-spinning of graphene fibers for high performance flexible supercapacitors}, volume={7}, ISSN={["2050-7496"]}, DOI={10.1039/c8ta12337c}, abstractNote={Al3+ coagulated wet-spun graphene fibers show a large surface area and high electrical conductivity, resulting in large capacitance.}, number={12}, journal={JOURNAL OF MATERIALS CHEMISTRY A}, author={He, Nanfei and Shan, Weitao and Wang, Julia and Pan, Qin and Qu, Jiangang and Wang, Guofeng and Gao, Wei}, year={2019}, month={Mar}, pages={6869–6876} }
 @article{qu_he_patil_wang_banerjee_gao_2019, title={Screen Printing of Graphene Oxide Patterns onto Viscose Nonwovens with Tunable Penetration Depth and Electrical Conductivity}, volume={11}, ISSN={["1944-8252"]}, url={http://dx.doi.org/10.1021/acsami.9b00715}, DOI={10.1021/acsami.9b00715}, abstractNote={Graphene-based e-textiles have attracted great interest because of their promising applications in sensing, protection, and wearable electronics. Here, we report a scalable screen-printing process along with continuous pad-dry-cure treatment for the creation of durable graphene oxide (GO) patterns onto viscose nonwoven fabrics at controllable penetration depth. All the printed nonwovens show lower sheet resistances (1.2-6.8 kΩ/sq) at a comparable loading, as those reported in the literature, and good washfastness, which is attributed to the chemical cross-linking applied between reduced GO (rGO) flakes and viscose fibers. This is the first demonstration of tunable penetration depth of GO in textile matrices, wherein GO is also simultaneously converted to rGO and cross-linked with viscose fibers in our processes. We have further demonstrated the potential applications of these nonwoven fabrics as physical sensors for compression and bending.}, number={16}, journal={ACS APPLIED MATERIALS & INTERFACES}, publisher={American Chemical Society (ACS)}, author={Qu, Jiangang and He, Nanfei and Patil, Shradha V. and Wang, Yanan and Banerjee, Debjyoti and Gao, Wei}, year={2019}, month={Apr}, pages={14944–14951} }
 @article{pan_tong_he_liu_shim_pourdeyhimi_gao_2018, title={Electrospun Mat of Poly(vinyl alcohol)/Graphene Oxide for Superior Electrolyte Performance}, volume={10}, ISSN={["1944-8252"]}, DOI={10.1021/acsami.7b14498}, abstractNote={Here, we describe an electrospun mat of poly(vinyl alcohol) (PVA) and graphene oxide (GO) as a novel solid-state electrolyte matrix, which offers better performance retention upon drying after infiltrated with aqueous electrolyte. The PVA-GO mat overcomes the major issue of conventional PVA-based electrolytes, which is the ionic conductivity decay upon drying. After exposure to 45 ± 5% relative humidity at 25 °C for 1 month, its conductivity decay is limited to 38.4%, whereas that of pure PVA mat is as high as 84.0%. This mainly attributes to the hygroscopic nature of GO and the unique nanofiber structure within the mat. Monolithic supercapacitors have been derived directly on the mat via a well-developed laser scribing process. The as-prepared supercapacitor offers an areal capacitance of 9.9 mF cm-2 at 40 mV s-1 even after 1 month of aging under ambient conditions, with a high device-based volumetric energy density of 0.13 mWh cm-3 and a power density of 2.48 W cm-3, demonstrating great promises as a more stable power supply for wearable electronics.}, number={9}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Pan, Qin and Tong, Ningjun and He, Nanfei and Liu, Yixin and Shim, Eunkyoung and Pourdeyhimi, Behnam and Gao, Wei}, year={2018}, month={Mar}, pages={7927–7934} }
 @article{he_yoo_meng_yildiz_bradford_park_gao_2017, title={Engineering biorefinery residues from loblolly pine for supercapacitor applications}, volume={120}, ISSN={["1873-3891"]}, DOI={10.1016/j.carbon.2017.05.056}, abstractNote={Recycling agricultural waste biomass into high-value-added products is of great importance to offset the cost of biofuel production. Here, we make biochar-based activated carbons (BACs) from loblolly pine chips via different carbonization recipes and chemical activations. BACs were then assembled into electrochemical double-layer capacitors (EDLCs) as electrode materials. Surprisingly, pyrolysis at lower temperatures (300 °C and 350 °C) rendered better electrochemical performance of BACs than those done at higher temperatures (500 °C and 700 °C). This is mainly due to the large surface area and high pore volume generated at the lower temperatures. Among all the pyrolysis recipes, flash pyrolysis at 300 °C produced the BAC with the highest specific capacitance (74 F g−1 at 20 mV s−1), exceeding the specific capacitance of commercial activated carbon (NORIT®) by 45%. This report demonstrates the great potential of our refinery recipe to engineer BACs from the sustainable, affordable, and abundant natural wastes for energy-storage applications, which opens the door for a group of biorefinery residues for value-added applications.}, journal={CARBON}, author={He, Nanfei and Yoo, Seunghyun and Meng, Jiajia and Yildiz, Ozkan and Bradford, Philip D. and Park, Sunkyu and Gao, Wei}, year={2017}, month={Aug}, pages={304–312} }
 @article{he_pan_liu_gao_2017, title={Graphene-Fiber-Based Supercapacitors Favor N-Methyl-2-pyrrolidone/Ethyl Acetate as the Spinning Solvent/Coagulant Combination}, volume={9}, ISSN={["1944-8244"]}, DOI={10.1021/acsami.7b05982}, abstractNote={One-dimensional flexible fiber supercapacitors (FSCs) have attracted great interest as promising energy-storage units that can be seamlessly incorporated into textiles via weaving, knitting, or braiding. The major challenges in this field are to develop tougher and more efficient FSCs with a relatively easy and scalable process. Here, we demonstrate a wet-spinning process to produce graphene oxide (GO) fibers from GO dispersions in N-methyl-2-pyrrolidone (NMP), with ethyl acetate as the coagulant. Upon chemical reduction of GO, the resulting NMP-based reduced GO (rGO) fibers (rGO@NMP-Fs) are twice as high in the surface area and toughness but comparable in tensile strength and conductivity as that of the water-based rGO fibers (rGO@H2O-Fs). When assembled into parallel FSCs, rGO@NMP-F-based supercapacitors (rGO@NMP-FSCs) offered a specific capacitance of 196.7 F cm-3 (147.5 mF cm-2), five times higher than that of rGO@H2O-F-based supercapacitors (rGO@H2O-FSCs) and also higher than most existing wet-spun rGO-FSCs, as well as those FSCs built with metal wires, graphene/carbon nanotube (CNT) fibers, or even pseudocapacitive materials. In addition, our rGO@NMP-FSCs can provide good bending and cycling stability. The energy density of our rGO@NMP-FSCs reaches ca. 6.8 mWh cm-3, comparable to that of a Li thin-film battery (4 V/500 μAh).}, number={29}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={He, Nanfei and Pan, Qin and Liu, Yixin and Gao, Wei}, year={2017}, month={Jul}, pages={24568–24576} }
 @article{he_yildiz_pan_zhu_zhang_bradford_gao_2017, title={Pyrolytic-carbon coating in carbon nanotube foams for better performance in supercapacitors}, volume={343}, ISSN={["1873-2755"]}, url={https://publons.com/publon/19584407/}, DOI={10.1016/j.jpowsour.2017.01.091}, abstractNote={Nowadays, the wide-spread adoption of supercapacitors has been hindered by their inferior energy density to that of batteries. Here we report the use of our pyrolytic-carbon-coated carbon nanotube foams as lightweight, compressible, porous, and highly conductive current collectors in supercapacitors, which are infiltrated with chemically-reduced graphene oxide and later compressed via mechanical and capillary forces to generate the active electrodes. The pyrolytic carbon coatings, introduced by chemical vapor infiltration, wrap around the CNT junctions and increase the surface roughness. When active materials are infiltrated, the pyrolytic-carbon coatings help prevent the π-stacking, enlarge the accessible surface area, and increase the electrical conductivity of the scaffold. Our best-performing device offers 48% and 57% higher gravimetric energy and power density, 14% and 23% higher volumetric energy and power density, respectively, and two times higher knee frequency, than the device with commercial current collectors, while the “true-performance metrics” are strictly followed in our measurements. We have further clarified the solution resistance, charge transfer resistance/capacitance, double-layer capacitance, and Warburg resistance in our system via comprehensive impedance analysis, which will shed light on the design and optimization of similar systems.}, journal={JOURNAL OF POWER SOURCES}, publisher={Elsevier BV}, author={He, Nanfei and Yildiz, Ozkan and Pan, Qin and Zhu, Jiadeng and Zhang, Xiangwu and Bradford, Philip D. and Gao, Wei}, year={2017}, month={Mar}, pages={492–501} }
 @article{wang_babaahmadi_he_liu_pan_montazer_gao_2017, title={Wearable supercapacitors on polyethylene terephthalate fabrics with good wash fastness and high flexibility}, volume={367}, ISSN={["1873-2755"]}, DOI={10.1016/j.jpowsour.2017.09.047}, abstractNote={All solid-state micro-supercapacitors (MSC) have emerged as attractive energy-storage units for portable and wearable electronics. Here, we describe a textile-based solid-state MSC via laser scribing of graphene oxide (GO) coatings on a flexible polyethylene terephthalate (PET) fabric. The laser-scribed graphene oxide layers (LGO) possess three-dimensionally porous structure suitable for electrochemical-double-layer formation. To improve the wash fastness and the flexibility of the as-prepared MSCs, glutaraldehyde (GA) was employed to crosslink the GO layers and PVA-gel electrolyte onto the PET fabric. The resultant all solid-state MSCs exhibited excellent flexibility, high areal specific capacitance (756 μF·cm−2 at 20 mV·s−1), and good rate capability when subject to bending and laundering. Furthermore, the MSC device showed a high power density of about 1.4 W·cm−3 and an energy density of 5.3 × 10−5 Wh·cm−3, and retained 98.3% of its initial capacitance after 1000 cycles at a current density of 0.5 mA·cm−2. This work is the first demonstration of in-plane MSCs on PET fabric surfaces with enhanced durability and flexibility.}, journal={JOURNAL OF POWER SOURCES}, author={Wang, Guixia and Babaahmadi, Vahid and He, Nanfei and Liu, Yixin and Pan, Qin and Montazer, Majid and Gao, Wei}, year={2017}, month={Nov}, pages={34–41} }
 @article{pan_chung_he_jones_gao_2016, title={Accelerated Thermal Decomposition of Graphene Oxide Films in Air via in Situ X-ray Diffraction Analysis}, volume={120}, ISSN={["1932-7455"]}, DOI={10.1021/acs.jpcc.6b05031}, abstractNote={Thermal decomposition of graphene oxide (GO) has been extensively investigated in the past decade, but the detailed reaction kinetics remains elusive so far. Here we employ an in situ X-ray diffraction (XRD) analysis to clarify the kinetics of GO decomposition in different atmospheres and sample morphologies. The XRD peak (002), which is the major diffraction peak corresponding to the interlayer distance in GO samples, shifted from 11.5° to 23° along with significant decrease in intensity when samples were heated from 25 to 350 °C. The decomposition in air exhibits a higher reaction rate compared with that in pure nitrogen gases because the O2 molecules in air facilitate the oxidation of carbon atoms, leading to the evolution of CO and CO2. Free-standing films of GO also decompose significantly faster than GO powders, owing to their slower heat dissipation into the environment and higher thermal conductivity within the well-stacked lamella. This study has provided new insights into the reaction kinetics o...}, number={27}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Pan, Qin and Chung, Ching-Chang and He, Nanfei and Jones, Jacob L. and Gao, Wei}, year={2016}, month={Jul}, pages={14984–14990} }
 @article{gao_havas_gupta_pan_he_zhang_wang_wu_2016, title={Is reduced graphene oxide favorable for nonprecious metal oxygen-reduction catalysts?}, volume={102}, ISSN={["1873-3891"]}, DOI={10.1016/j.carbon.2016.02.054}, abstractNote={Reduced graphene oxide (rGO), as a newly emerged carbon material, has attracted great attention concerning its applications for electrocatalysts. Presently, there are mixed opinions regarding the advantages to using rGO as a support for preparing nonprecious metal catalysts for the oxygen reduction reaction (ORR). The primary goal of this work is to determine whether rGO would be favorable for non-precious metal catalysis of oxygen reduction or not. In the case of Fe-free catalysts, when polyaniline (PANI) was used as nitrogen/carbon precursor, the PANI-rGO catalyst is superior to the PANI-Ketjenblack (KJ) carbon black catalyst in terms of ORR activity and H2O2 yield. When comparing the ORR activity of PANI-Fe-rGO to the traditional PANI-Fe-KJ, in more challenging acidic electrolyte, PANI-Fe-rGO performed no better than PANI-Fe-KJ. However, rGO does indeed enhance stability of the Fe–N–C catalyst in acidic media. In addition, in an alkaline electrolyte, ORR activity was significantly improved when using rGO in comparison to the KJ-supported Fe–N–C catalysts. Based on detailed comparisons of structures, morphologies, and reaction kinetics, the traditional KJ support with dominant microporous is able to accommodate more FeNx moieties that are crucial for the ORR in acid. Oppositely, the richness of nitrogen-doped graphene edge sites provided by rGO facilitates the ORR in the alkaline electrolyte.}, journal={CARBON}, author={Gao, Wei and Havas, Dana and Gupta, Shiva and Pan, Qin and He, Nanfei and Zhang, Hanguang and Wang, Hsing-Lin and Wu, Gang}, year={2016}, month={Jun}, pages={346–356} }