Surface Defect Density Research Articles

Current transport properties of Pt/n-GaN Schottky diodes with ZnO interlayers

In this work, atomic layer deposition (ALD) was used to grow 20-nm thick ZnO interlayers (IL) on a GaN substrate at 150 and 200 °C and the current transport mechanisms of vertical Pt/ZnO/n-GaN Schottky diodes were investigated. A high density of surface state was observed for the ZnO layer grown at 200 °C. An analysis of the forward current–voltage (I–V) data considering various transport mechanisms demonstrated that the thermionic emission and the tunneling components attributed to the total current for the ZnO layer grown at 150 °C. In contrast, it was observed that the tunneling component mainly caused the current conduction in the ZnO layer grown at 200 °C. Additionally, an analysis of the reverse I–V characteristics exhibited a high density of surface defects on the ZnO layer grown at 200 °C. This study demonstrated that the ALD growth temperature of ZnO IL significantly affects the I–V characteristics of GaN Schottky diodes.

LaTiO2N nanopowders (NPs) with low surface defect density via nitridation of flame made NPs retaining simple perovskite structure.

This work introduces a novel route to perovskite LaTiO2N nanopowders (NPs) via nitridation of perovskite LaTiO3 NPs in an NH3 gas flow at 1050 °C/NH3/15 h, in which a simple perovskite structure (ABX3) is retained during nitridation. The LaTiO3 NP is formed with a trace of a second phase in a precursor oxide NP (LTO-4/3) produced using liquid-feed flame spray pyrolysis (LF-FSP) of a metallo-organic ethanol solution with La/Ti = 4/3. The characterization of the resulting powders allows for a comparison with LaTiO2N NPs synthesized by the nitridation of the La2Ti2O7 precursor oxide NP (LTO-1) with a perovskite slab structure (A2B2X7) also prepared by LF-FSP of a La/Ti = 1 solution. Williamson-Hall plots suggest that the as-produced LaTiO2N from LTO-1 offers a quite small but effective crystallite size of 16-18 nm with almost no lattice spacing fluctuations, while LaTiO2N from LTO-4/3 presents a larger effective crystallite size of 50-52 nm with some lattice spacing fluctuations. UV-vis diffuse reflectance analysis reveals that, unlike LaTiO2N from LTO-1, the spectra of LaTiO2N from LTO-4/3 show a quite low absorptionbackground above the wavelength of the optical absorption edge (∼580 nm), suggesting good crystallinity with a very low surface defect density. Both oxynitride NPs appear to offer utility as inorganic pigments with different colours, while LaTiO2N NPs from LTO-4/3 have advantages for various applications, including potential as a visible-light-driven water splitting photocatalyst.

Controllable morphology of Bi2S3nanostructures formedviahydrothermal vulcanization of Bi2O3thin-film layer and their photoelectrocatalytic performances

AbstractBi2S3nanostructures with various morphologies were synthesized through hydrothermal vulcanization at different sulfur precursor (thiourea) concentrations. A 100 nm thick sputter-deposited Bi2O3thin-film layer on a fluorine-doped tin oxide glass substrate was used as a sacrificial template layer. The etching of the Bi2O3sacrificial template layer and the regrowth of Bi2S3crystallites during hydrothermal vulcanization produced the different Bi2S3nanostructure morphologies. The lowest sulfur precursor concentration (0.01 M) induced the formation of Bi2S3nanosheets, whereas the Bi2S3nanoribbons and nanowires were formed with increased sulfur precursor concentrations of 0.03 and 0.1 M, respectively. These results indicate that sputter-deposited Bi2O3thin-film layers can be effectively used to form low-dimensional Bi2S3crystals with controllable morphologies. Among the various Bi2S3samples, the Bi2S3nanosheets exhibited superior photoactive ability. The higher active surface area, surface defect density, light absorption capacity, and photo-induced charge separation ability of Bi2S3nanosheets explain their superior photoelectrocatalytic degradation ability of rhodamine B dyes.

Defect engineering on the defluorinated MWCNTs@SnO2@N-doped carbon composite for enhanced lithium storage performance

When tin oxide (SnO 2 ) is used in the anode of lithium-ion batteries, its capacity decreases dramatically due to poor conductivity and volume effects during the electrochemical cycle. Although composites with traditional carbon-based materials can improve this shortcoming, the low capacitance of such materials still limits the capacity of the composites. Therefore, we applied defect engineering to SnO 2 /C composite electrodes for the first time, and prepared D-MWCNTs@SnO 2 @N–C composite electrodes with hollow rod structures. Defects were constructed in the carbon materials to promote electron diffusion and ion storage active sites. The hollow structure can adapt to the volume change that occurs during Li-ion insertion/desorption. In addition, the detachment of F atoms and the insertion of N atoms, which are chemical processes that occur on the surface of carbon materials, promote an increase in surface porosity and defect density, thereby providing additional lithium storage sites. The double carbon effect caused by defect engineering provides a multidimensional transport path and rapid migration rate for Li-ions, which enables the electrode to display excellent electrochemical performance; thus, this work could lead to the preparation of next-generation anode materials with high energy storage capacity, high rate capability and high cycle stability.

High efficient adsorption and photocatalytic removal of hexavalent chromium over three-dimensional grapheneoxide aerogel under visible light

<p indent="0mm">Heavy metal ions such as hexavalent chromium (Cr(VI)) existed in wastewater have caused serious pollution problems.Cr(VI) is teratogenic and carcinogenic, while trivalent chromium (Cr(III)) is an essential nutrient for humans and animals. Adsorption method can transfer Cr(VI) from liquid phase to absorbent surface, but it needs follow-up treatment to remove Cr(VI). Photocatalysis technique can reduce Cr(VI) to Cr(III), so as to decrease its toxicity, but the adsorption capacity towards Cr(VI) is always small due to poor surface area of some traditional semiconductor oxide photocatalysts. Therefore, a new material with both good adsorption capacity and photocatalytic activity is needed for Cr(VI) removal. As an emerging kind of carbon materials, graphene oxide (GO) has attracted particular attention in the catalysis field. Graphene oxide aerogel (GOA), a three dimensional nanomaterial, possesses numerous adsorption sites and superior ability to accept and transport photogenerated electrons, would thus present good adsorption capacity and high photocatalytic performance simultaneously. So far, most studies on GO-base material are towards investigating its co-catalyst role (adsorption enhancement or electron shuttle) in improving efficiency of metal or semiconductor photocatalysts. Only a few studies have applied GO-base material as a sole photocatalyst. In this study, combined with the cross-linking method and the supercritical CO₂ fluid extraction method, three-dimensional porous and recyclable GOA with large specific surface area and defect sites was prepared by using GO as the precursor. The physicochemical properties were characterized by SEM, XRD, Raman spectroscopy and nitrogen adsorption methods. The adsorption behavior and photocatalytic reduction performance of GOA towards Cr(VI) under visible light were investigated. GO was hydrothermally reduced during the preparation process, and many defects were generated on GO sheets. Melamine and cyanuric acid were used as crosslinking agents to increase the interlayer spacing, and at the same time providing GOA a large specific surface area and a rich porous structure. When the mass ratio of GO, melamine, and cyanuric acid was 3:3:3 and the GO concentration was 6 mg L⁻¹, GOA exhibited the largest specific surface area and defect density. This kind of GOA, i.e., GOA_333-6 presented the best adsorption capacity and photocatalytic efficiency of Cr(VI). The adsorption behavior of GOA on Cr(VI) fits to the quasi-second-order kinetic model and the Langmuir adsorption isotherm model, indicating that the adsorption process was a single-layer chemical adsorption, in which the intra-particle diffusion in the initial adsorption stage was the rate-limiting step. The three-dimensional graphene oxide aerogel GOA obtained in this study exhibited large adsorption capacity, high photocatalytic removal efficiency for high concentration Cr(VI) under visible light, and good repeatability. Single GOA material has potential application in removing heavy metal ions from polluted wastewater.

Structure-Activity Relationship of Graphene-Based Materials: Impact of the Surface Chemistry, Surface Specific Area and Lateral Size on Their In Vitro Toxicity.

Predictive toxicity and structure–activity relationships (SARs) are raising interest since the number of nanomaterials has become unmanageable to assess their toxicity with a classical case-by-case approach. Graphene-based materials (GBMs) are among the most promising nanomaterials of this decade and their application might lead to several innovations. However, their toxicity impact needs to be thoroughly assessed. In this regard, we conducted a study on 22 GBMs to investigate their potential SARs by performing a complete physicochemical characterization and in vitro toxicity assessment (on RAW264.7 cells). We used GBMs of variable lateral size (0.5–38 µm), specific surface area (SSA, 30–880 m²/g), and surface oxidation (2–17%). We observed that reduced graphene oxides (RGOs) were more reactive than graphene nanoplatelets (GNPs), potentially highlighting the role of GBM’s surface chemistry and surface defects density in their biological impact. We also observed that for GNPs, a smaller lateral size caused higher cytotoxicity. Lastly, GBMs showing a SSA higher than 200 m²/g were found to induce a higher ROS production. Mechanistic explanations are proposed in the discussion. In conclusion, pairing a full physicochemical characterization with a standardized toxicity assessment of a large set of samples allowed us to clarify SARs and provide an additional step toward safe-by-design GBMs.

Role of nanoscale surface defects on Sn adsorption and diffusion behavior on oxidized Nb(100)

Nanoscale structural defects such as grain boundaries, atomic dislocations, and surface roughness inhibit the stoichiometrically homogeneous growth of Nb3Sn on Nb. This is a critical technological bottleneck for the implementation of next-generation Nb3Sn superconducting radio frequency cavities, as thin film inhomogeneities are known to degrade superconducting properties that are essential for reaching optimal cavity performance. To determine the influence of structural defects on Nb3Sn film growth, low and moderate surface defect densities were intentionally induced onto a (3 × 1)-O Nb(100) substrate, which serves as a model system to study atomic-scale Sn adsorption and diffusion. Scanning tunneling microscopy shows that, while initial Sn adsorption behavior at room temperature differs between the low and moderate defect density Nb(100) surfaces, the overall diffusion pathways at elevated temperatures are guided by the underlying oxide structure with variations resulting from increased nanoscale surface defects. The (3 × 1)-O Nb(100) surface with a moderate defect density also demonstrates enhanced Sn thermal stability, with the Sn desorption threshold occurring between 850 and 900 °C, approximately 50 °C higher than desorption from both the low defect density and pristine thin oxide surfaces. This suggests that structural surface defects may stabilize adsorbed Sn species on oxidized Nb at the elevated temperatures utilized in Nb3Sn alloy growth procedures. Auger electron spectroscopy shows no significant difference in surface composition following Sn deposition at varying coverages on the pristine and defect-induced (3 × 1)-O Nb(100) surfaces. This indicates that the surface and near-surface composition are not influenced by the presence of nanoscale surface defects despite slight attenuations in Sn diffusion pathways on defected substrates. These results provide the first in situ visualization of Sn adsorption and diffusion behavior on oxidized Nb at the nanoscale, revealing the significance of the underlying Nb oxide surface structure and defect density on Nb3Sn film growth and, ultimately, cavity performance.

Microstructure evolution and mechanical behavior of a mullite fiber heat‐treated from 1100 to 1300°C

AbstractIn this paper, the effect of phase transformation on microstructure evolution and mechanical behaviors of mullite fibers was well investigated from 1100 to 1300°C. In such a narrow temperature range, the microstructure and mechanical properties showed great changes, which were significant to be studied. The temperature of the alumina phase transformation started at below 1100°C. The main phases in fibers were γ‐Al2O3 and δ‐Al2O3 with amorphous SiO2 at 1150°C. The stable α‐Al2O3 formed at 1200°C. Then the mullite phase reaction occurred. As the alumina phase reaction took place, the tensile strength increased with the increasing temperature. In particular, the filaments achieved the highest strength at 1150°C with 1.98 ± 0.17 GPa, and the Young's modulus was 163.08 ± 4.69 GPa, showing excellent mechanical performance. After 1200°C, the mullite phase reaction went on with the crystallization of orthorhombic mullite. The density of surface defects increased rapidly due to thermal grooving, which led to mechanical properties degrade sharply. The strength at 1200°C was 1.01 ± 0.15 GPa with a strength retention of 63.13%, and the Young's modulus was 184.14 ± 10.36 GPa. While at 1300°C, the tensile strength was 0.64 ± 0.14 GPa with a strength retention of only 40.00%.

Molecular passivation of MAPbI3 perovskite films follows the Langmuir adsorption rule

Surface defect passivation through additional molecular bonding plays a crucial role in optimization of perovskite-based photovoltaic devices. So far, quantization of the defect site coverage by molecular passivation remains unclear from a macroscopic view. We herein unravel the coverage possibility of the surface defect sites of perovskite films by the added molecule passivators upon an MAPbI3 perovskite system. Concerns of inconsistent time-resolved photoluminescence (TRPL) spectroscopic measurements are dispelled by vapor-deposition fabrications of highly uniform perovskite films. The surface defect densities of perovskite films are derived from global fittings of the charge carrier dynamics to the measured TRPL decays. It is revealed the Langmuir adsorption relationship of the defect site coverage with respect to the added amount of tri-n-octylphosphine oxide passivation molecules. Our work supplements the dynamical bonding model of the molecular passivation process and provides reliable knowledge upon the bonding process between molecules and defects, which leads to rationalized surface passivation methodologies in perovskite photovoltaics communities.

Role of dissolved CO in the solution on the origin of CO pre-oxidation on Pt(1 1 1)-Type electrodes

• CO pre-oxidation occurs on (1 1 1) terrace sites of catalyst surfaces defect-rich. • CO in solution determines the magnitude (and the shape of the curve) of CO pre-oxidation. • CO pre-oxidation involves the diffusion-limited bulk CO electro-oxidation at most active sites. • Main CO electro-oxidation peak is a typical behavior of a surface-confined process. In voltammetric CO stripping experiments in acid media, CO pre-oxidation usually takes place on catalysts with a high density of surface defects, obeyed the conditions of full CO ads layer formation at suitable low potentials into the “hydrogen region” and, importantly, CO traces in the bulk of the solution is required. This study aims to interrogate that. The electro-oxidation of CO was voltammetrically conducted applying different scan rates, employing Pt(1 1 1) terraced surfaces and full CO coverage equilibrated with different content of dissolved CO in the bulk of an acid quiescent solution; also experiments were performed in which CO ads was present only on the (1 1 0)-type steps in a CO-free solution. It was found that: (1) slopes of peak potentials of CO pre-oxidation versus the logarithm of scan rates were smaller for higher CO contents in the solution; (2) charge density of CO pre-oxidation was higher for slower scan rate; (3) CO pre-oxidation takes place at low potentials where the (1 1 0)-type step sites were inactive in the catalysis of CO electro-oxidation. We conclude that, in such a quiescent solution, the content of dissolved CO in the bulk of the solution determines the magnitude and the shape of the curve of the CO pre-oxidation. This can be understandable in terms of prompt provision of CO molecules from the solution (diffusion layer) to surface active sites, that is, the most active sites, released during the CO pre-oxidation. In the CO pre-oxidation on Pt(1 1 1) terraced surfaces, the most active sites lie at the bottom of (1 1 1) terraces adjacent to the steps. The results provide evidence that, in presence of CO traces in the bulk of the solution, on one hand, the pre-oxidation of CO involves the diffusion-limited electro-oxidation of bulk CO at most active sites released during the CO pre-oxidation . On the other hand, the main CO electro-oxidation peak is a typical behavior of a surface-confined process. Our proposition applies to Pt electrodes in acidic medium.

The effect of oxygen annealing on characteristics of β-Ga2O3 solar-blind photodetectors on SiC substrate by ion-cutting process

In this work, a high quality (2̅01) β-Ga2O3 single-crystalline film was transferred to the 4H-SiC substrate by ion-cutting technique, on which the metal-semiconductor-metal (MSM) solar-blind photodetectors (PDs) were fabricated. The effect of the oxygen annealing on the performance of PDs has been systematically studied. The PD fabricated on the as-transferred film exhibits a high responsivity (R) of 2.24 A/W with a large external quantum efficiency of 1.21 × 103%, and an ultrahigh responsivity rejection ratio (R240nm/R350nm) of 1.02 × 105. In comparison, the PD based on the β-Ga2O3 film annealed in oxygen atmosphere exhibits a reduced dark current of 0.6 nA at the bias of 5 V, a fast decay time of 41 ms but a relatively reduced internal gain. It is resulted from the increased Schottky barrier height and the suppression of persistent photoconductivity effect due to the reduced density of surface oxygen vacancies and defects upon annealing. These results would promote a better understanding of dark current and responsivity of PDs modulated by oxygen annealing.

Microstructural and mechanical characterization of a mullite fiber

The effect of thermal exposure on a mullite fiber was analyzed. This type of mullite fiber, consisting of γ-Al2O3 and amorphous SiO2, was developed for high-temperature applications. Heat treatments at temperatures ranging from 900 °C to 1500 °C for 1h were performed in air. Investigations showed that the tensile strength of the initial fiber was about 1.60 GPa. And the elastic modulus was about 133.51 GPa. The bundles’ strength decreased at 900 °C slightly after thermal treatment, then increased and got a maximum at 1100 °C with 1.65 GPa. At above 1100 °C, the strength degraded sharply due to the mullite phase transformation and the exaggerated grain growth. At 1300 °C, the phase reaction almost finished with a tensile strength of 0.86 GPa. And the strength retention was only 47.50%. When the heat-treated temperature got to 1500 °C, the density of surface defects in the fiber surged, making it too fragile and weak to go through the tensile tests.

Highly efficient Pt catalyst on newly designed CeO2-ZrO2-Al2O3 support for catalytic removal of pollutants from vehicle exhaust

Pt-CeO2 catalysts have been widely studied for the vehicle emission control. Designing novel CeO2 based supports with improved physical-chemical properties has become a research hotspot to further promote the catalytic performance and stability of Pt-CeO2 catalysts. In this work, through utilizing a unique, two-step incipient wetness impregnation (T-IWI) method for ceria-zirconia-alumina (CZA-T) support preparation, a Pt single site catalyst (Pt/CZA-T) with excellent thermal stability was synthesized. Higher oxidation activity and Oxygen storage capacity (OSC) were achieved on activated Pt/CZA-T, comparing to Pt catalysts on regular CeO2/Al2O3 (Pt/CA) and one-step prepared CeZrOx/Al2O3 (Pt/CZA). Via the modification of hydrophilic/hydrophobic properties of γ-Al2O3 by this unique T-IWI method, finer Ce0.9Zr0.1O2 particles with higher density of surface defects were formed on CZA-T, on which a higher Pt dispersion and stronger Pt-O-Ce interaction were achieved. Upon activation, smaller, well-dispersed Pt clusters on CZA-T were generated. It was concluded that the CO oxidation performance and OSC were highly related to the size of Pt clusters on different supports that we have developed. More Pt sites located at Pt cluster-CeZrOx interfaces, which were the real active sites, were responsible for the highest OSC function and CO oxidation activity of activated Pt/CZA-T catalyst.

Numerical Design of Ultrathin Hydrogenated Amorphous Silicon-Based Solar Cell

Numerical modelling is used to confirm experimental and theoretical work. The aim of this work is to present how to simulate ultrathin hydrogenated amorphous silicon- (a-Si:H-) based solar cells with a ITO BRL in their architectures. The results obtained in this study come from SCAPS-1D software. In the first step, the comparison between the J-V characteristics of simulation and experiment of the ultrathin a-Si:H-based solar cell is in agreement. Secondly, to explore the impact of certain properties of the solar cell, investigations focus on the study of the influence of the intrinsic layer and the buffer layer/absorber interface on the electrical parameters ( J SC , V OC , FF, and η ). The increase of the intrinsic layer thickness improves performance, while the bulk defect density of the intrinsic layer and the surface defect density of the buffer layer/ i -(a-Si:H) interface, respectively, in the ranges [109 cm-3, 1015 cm-3] and [1010 cm-2, 5 × 10 13 cm-2], do not affect the performance of the ultrathin a-Si:H-based solar cell. Analysis also shows that with approximately 1 μm thickness of the intrinsic layer, the optimum conversion efficiency is 12.71% ( J SC = 18.95 mA · c m − 2 , V OC = 0.973 V , and FF = 68.95 % ). This work presents a contribution to improving the performance of a-Si-based solar cells.

W[sbnd]O bond shortening by doping of first-row transition metal ions that enhances its catalytic potency

Here, we report thorough spectroscopic characterization of tungsten oxide (WO3) nanoparticles (NPs) and WO3 NPs surface doped with transition metal (TM) ions (TM@WO3; TM = Cr3+, Mn2+, Fe3+, Co2+, and Ni2+) by using various surface analysis techniques such as transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), high-resolution X-ray photoelectron spectroscopy (HRXPS), and extended X-ray absorption fine structure (EXAFS). At first glance, the morphologically distinct features were not perceivable across TM dopants. However, the detailed XPS analysis confirmed that the WO3 NPs doped with Cr and Fe ions formed a relatively large number of surface defects. Moreover, we found through EXAFS analysis that the chromium and iron ions doping on WO3 NPs promoted the dramatic shortening of the WO bond length as compared to pristine WO3 and other metal ion doped WO3 NPs. Much enhanced photocatalytic and electrocatalytic activities of Cr@WO3 and Fe@WO3, which relied on the different density of surface defects created by the charge and size of the TM dopants, were demonstrated in the photocatalytic degradation reactions of 4-chlorophenol and the electrocatalytic hydrogen evolution reaction. The present result can serve as a practical guideline for atomically precise control of oxygen vacancy toward the development of high-performance metal oxide photocatalysts.

Alleviating halide perovskite surface defects

Alleviating halide perovskite surface defects

Electrical Loss Management by Molecularly Manipulating Dopant-free Poly(3-hexylthiophene) towards 16.93 % CsPbI2 Br Solar Cells.

Inorganic cesium lead halide perovskites offer a pathway towards thermally stable photovoltaics. However, moisture-induced phase degradation restricts the application of hole transport layers (HTLs) with hygroscopic dopants. Dopant-free HTLs fail to realize efficient photovoltaics due to severe electrical loss. Herein, we developed an electrical loss management strategy by manipulating poly(3-hexylthiophene) with a small molecule, i.e., SMe-TATPyr. The developed P3HT/SMe-TATPyr HTL shows a three-time increase of carrier mobility owing to breaking the long-range ordering of "edge-on" P3HT and inducing the formation of "face-on" clusters, over 50 % decrease of the perovskite surface defect density, and a reduced voltage loss at the perovskite/HTL interface because of favorable energy level alignment. The CsPbI2 Br perovskite solar cell demonstrates a record-high efficiency of 16.93 % for dopant-free HTL, and superior moisture and thermal stability by maintaining 96 % efficiency at low-humidity condition (10-25 % R. H.) for 1500 hours and over 95 % efficiency after annealing at 85 °C for 1000 hours.

Electrical Loss Management by Molecularly Manipulating Dopant‐free Poly(3‐hexylthiophene) towards 16.93 % CsPbI2Br Solar Cells

AbstractInorganic cesium lead halide perovskites offer a pathway towards thermally stable photovoltaics. However, moisture‐induced phase degradation restricts the application of hole transport layers (HTLs) with hygroscopic dopants. Dopant‐free HTLs fail to realize efficient photovoltaics due to severe electrical loss. Herein, we developed an electrical loss management strategy by manipulating poly(3‐hexylthiophene) with a small molecule, i.e., SMe‐TATPyr. The developed P3HT/SMe‐TATPyr HTL shows a three‐time increase of carrier mobility owing to breaking the long‐range ordering of “edge‐on” P3HT and inducing the formation of “face‐on” clusters, over 50 % decrease of the perovskite surface defect density, and a reduced voltage loss at the perovskite/HTL interface because of favorable energy level alignment. The CsPbI2Br perovskite solar cell demonstrates a record‐high efficiency of 16.93 % for dopant‐free HTL, and superior moisture and thermal stability by maintaining 96 % efficiency at low‐humidity condition (10–25 % R. H.) for 1500 hours and over 95 % efficiency after annealing at 85 °C for 1000 hours.

Interplay between Copper Nanoparticle Size and Oxygen Vacancy on Mg-Doped Ceria Controls Partial Hydrogenation Performance and Stability

A series of CunCeMgOx catalysts with various copper nanoparticle sizes and surface defect densities were synthesized and tested for partial hydrogenation of 1,3-butadiene (1,3-BD). The data demonst...

Synthesis of size-controlled carbon microspheres from resorcinol/formaldehyde for high electrochemical performance

Nanostructured phenolic resin-based carbon aerogels with an extensive network structure are regarded as ideal energy storage materials for supercapacitors. However, the initial bulk form and low capacitance of previously reported porous carbon aerogels are problematic for practical use. Phenolic resin-based porous carbon spheres were synthesized by a simple hydrothermal process using ammonia, ethylenediamine or hexylenediamine as a catalyst. The porous carbon spheres were investigated by SEM, BET, XPS, etc. It was found that the number of ammonium groups, length of the alkyl chain and processing temperature play vital roles in determining the pore structure, size and uniformity of the carbon spheres. NH4+ is necessary to obtain the carbon spheres and but changing the other parameters has no obvious effect on their crystal structure. The sample prepared at a hydrothermal temperature of 80 °C using ammonia as the catalyst has the highest specific capacitance of 233.8 F g−1 at a current density of 1.0 A g−1. It has an excellent capacitance retention of 98% after 10,000 charge/discharge cycles at 7 A g−1, indicating its good cycling stability and rate capability. This result shows that a higher specific surface area, porosity and defect density are probably the crucial factors in improving the electrochemical capacitance.