Negligible Current Density Research Articles

Analyzing the composite heterostructure as an efficient electrolyte for low-temperature ceramic fuel cells

The hexagonal wurtzite structure (ZnO) is a well-known multifunctional semiconductor, and it is widely used as an electrolyte in energy applications such as fuel cells. ZnO, an n-type semiconductor, can be used as the electrolyte in fuel cells despite its insufficient open circuit voltage and negligible current density. After incorporating GDC to create a semiconductor ionic GDC/ZnO heterostructure, the ionic conductivity increased to 0.16 S/cm, and the fuel cell performance improved to 802 mW/cm2 at 520 °C. It has been discovered that the heterostructure's energy band bending and built-in electric field play a crucial role in the ionic transport and inhibiting the electronic conduction of GDC/ZnO, resulting in a notable material ionic property and fuel cell performance. Also, relaxation time distribution analysis revealed that interfacial conduction plays a significant role in the ionic conduction of GDC/ZnO. These results indicate that ZnO, which has a wide bandgap, may be tailored to an ionic conducting electrolyte for fuel cell applications using a heterostructure approach and energy band alignment method.

Effects of Electrical Parameters on Micro-Arc Oxidation Coatings on Pure Titanium.

The micro-arc oxidation process was used to apply a ceramic oxide coating on a pure titanium substrate using calcium acetate and sodium dihydrogen phosphate as an electrolyte. The influence of the current frequency and duty ratio on the surface morphology, phase composition, wear behavior, and corrosion resistance were analyzed by employing a scanning electron microscope, X-ray diffractometer, ball-on-disk apparatus, and potentiodynamic polarization, respectively. Analyses of the surface and cross-sectional morphologies revealed that the MAO films prepared via a low current frequency (100 Hz) and a high duty ratio (60%) had a lower porosity and were more compact. The medium (500 Hz) and high (1000 Hz) frequencies at the higher duty ratios presented with better wear resistance. The highest film thickness (11.25 µm) was achieved at 100 Hz and a 20% duty ratio. A negligible current density was observed when the frequency was fixed at 500 Hz and 1000 Hz and the duty cycle was 20%.

Investigation of the current density’s non-uniform distribution in dead-end PEMFC with multi-zone measurement methods

Uneven current density distribution in a proton exchange membrane fuel cell (PEMFC) can decrease the reactant and catalyst utilization, reduce the energy conversion efficiency of the whole fuel cell, and even lead to a shortened cell life. Therefore, studying current density distribution has a critical role in the research and development of PEMFC. To investigate the distribution of the proton exchange membrane fuel cells' local current density under different operating conditions, a single cell using the segmented cell technique consisting of 36 zones was designed. The results show that the maximum current density first appears at the outlet and then moves to the inlet. In addition, when the cell output is stable, the most negligible current density appears in the cell's middle area. The current density distribution was improved when the cell temperature was 50 °C. Compared with other operation temperatures (without cooling, 40 °C, 60 °C), the current density is decreased by 14.0 %, 9.8 %, and 40.6 %, respectively. At the same time, the cell voltage is increased by 10 %, 6.45 % and 22.22 %, respectively. Higher gas pressure is more favourable to improving cell performance and the uniformity of current density distribution. However, when the cathode gas pressure exceeds that of the anode, the reverse inverse current is pronounced in the middle of the cell at the starting process. The reverse duration of the 50 °C cell is reduced by 30 s (25.4 %) compared to the cell without cooling.

2D BiSeI Nanosheets for Broadband Self‐Powered Photoelectrochemical Photodetector

Broadband photodetectors are essential for the integrated design of next‐generation optical detector devices. Ternary 2D bismuth sulfide semiconductor (BiXI, X = S, Se, Te) is an ideal candidate for broadband photoelectric detection due to its narrow bandgap and excellent electrical transport performance. Here, BiSeI is grown by chemical vapor transport (CVT) method and used in photoelectrochemical (PEC) photodetection. The PEC‐type photodetector based on BiSeI nanosheets has a broadband detection ranging from 350 to 900 nm, displaying a high responsivity of 2.88 mA W−1, a high detectivity of 1.10 × 1010 Jones and a fast response time of 7/16 ms at a bias voltage of 0.5 V. Furthermore, the device also exhibits a negligible current density loss after three months, which indicates that it has good stability against air and moisture. In addition, the photodetector can work without bias potential, indicating that it is a good self‐powered device. The results demonstrate that BiSeI is a potential material in self‐powered PEC photodetector.

Novel core-shell structured electrocatalyst with 1D-NiTe2 over 3D metal structure for efficient hydrogen evolution reactions

Novel inexpensive materials are the focus of modern research for efficient hydrogen evolution reactions (HER) to substitute scarce and expensive platinum (Pt) based electrocatalysts. The ideal material should be durable, low-cost, efficient and possess high surface area. Earth abundant Transition metal dichalcogenides (TMDCs) are the potential group of materials for providing inexpensive source of durable HER catalysts with high surface area and active edges due to their layered structure. Here, we report a scalable single-step microwave-assisted solution phase synthesis of NiTe2 with core-shell configuration over porous three-dimensional nickel foam (3D-NF). This surface heterojunction catalyst possesses high surface area, unique needlelike morphology, and efficient performance for hydrogen evolution reactions. NiTe2 needles decorated on porous 3D-NF displayed fast HER kinetics with a reasonable overpotential of ~ −0.36 V to drive a current density of 100 mA cm−2. A small Tafel slope of ~55 mV dec−1 is observed. The catalyst showed higher stability with negligible performance degradation even after 8 h of potential cycling operation. It also demonstrated negligible current density variation at a constant applied potential for more than 15 h in 0.5 M sulfuric acid (H2SO4) solution. The 3D porous skeleton allowed high impregnation of electrolyte while the dense needlelike morphology provided high surface area and active edge sites for reactions. A thin 7 nm of amorphous oxide overlayer shell on highly crystalline NiTe2 core structure makes it a surface heterojunction catalyst (SHC) which is reported to facilitate hydrogen desorption upon charge take up and makes it an efficient electrocatalyst.

High-efficiency electrocatalytic NO reduction to NH3by nanoporous VN

Electrocatalytic NO reduction reaction to generate NH₃ under ambient conditions offers an attractive alternative to the energy-extensive Haber–Bosch route; however, the challenge still lies in the development of cost-effective and high-performance electrocatalysts. Herein, nanoporous VN film is first designed as a highly selective and stable electrocatalyst for catalyzing reduction of NO to NH₃ with a maximal Faradaic efficiency of 85% and a peak yield rate of 1.05 × 10^–7 mol·cm^–2·s^–1 (corresponding to 5,140.8 μg·h^–1·mg_cat.^–1) at –0.6 V vs. reversible hydrogen electrode in acid medium. Meanwhile, this catalyst maintains an excellent activity with negligible current density and NH₃ yield rate decays over 40 h. Moreover, as a proof-of-concept of Zn–NO battery, it delivers a high power density of 2.0 mW·cm^–2 and a large NH₃ yield rate of 0.22 × 10^–7 mol·cm^–2·s^–1 (corresponding to 1,077.1 μg·h^–1·mg_cat.^–1), both of which are comparable to the best-reported results. Theoretical analyses confirm that the VN surface favors the activation and hydrogenation of NO by suppressing the hydrogen evolution. This work highlights that the electrochemical NO reduction is an eco-friendly and energy-efficient strategy to produce NH₃.

α-MoB2 Nanosheets for Hydrogen Evolution in Alkaline and Acidic Media

α-MoB2 is recognized as the most efficient molybdenum boride for electrocatalytic hydrogen evolution reaction (HER). However, the convenient synthesis of single phase α-MoB2 is still challenging, and its HER activity in alkaline electrolytes remains unclear. Herein, we report the first successful synthesis of the α-MoB2 nanosheets by a simple and facile molten salt method through the MoCl5 and NaBH4 reaction at 850 °C. The α-MoB2 nanosheets exhibit a remarkable HER performance in alkaline electrolytes, delivering a low overpotential of 124 mV at a current density of 10 mA/cm2. In acidic electrolytes, an improved performance was found in comparison to that of the bulk and nano α-MoB2 with an overpotential as low as 141 mV at 10 mA/cm2. Such HER performance arises from the nanosheet structure that allows more active planes to be exposed. In addition, the α-MoB2 nanosheets possess an outstanding stability in both acidic and alkaline media, showing negligible current density drop even after 3000 cycles and more than 24 h of potentiostatic operation.

Self-assembly of Au/MoS2 quantum dots core-satellite hybrid as efficient electrocatalyst for hydrogen production

Ultra-small MoS2 quantum dots (QDs) with an average size of 2.48 nm coated on Au nanoparticles with a core-satellite structure (Au/MoS2 QDs) are successfully prepared by a self-assembly strategy through the strong bonding between Au and S. Benefited from the unique structure, the Au/MoS2 QDs hybrid exhibits outstanding electrocatalytic performance toward hydrogen evolution reaction (HER). The Au/MoS2 QDs hybrid needs overpotentials of 112, 146, and 206 mV to approach current densities of 10, 20, and 50 mA·cm−2 in 0.5 mol·L−1 H2SO4 (pH = 0.3), respectively. And a low Tafel slope (83 mV·dec−1) is obtained. The catalyst also displays satisfactory stability and durability, indicating a negligible current density loss after 20 h of electrolysis. The high hydrogen generation activities and stability are attributed to the great number of active sites, high conductivity and synergistic effects between gold nanoparticles (Au NPs) and MoS2 QDs. Last but not least, this strategy opens up a favorable way to combine MoS2 QDs with other metals.

Oxygen doped MoS2 quantum dots for efficient electrocatalytic hydrogen generation.

In this study, we report an oxygen-doped MoS2 quantum dot (O-MoS2 QD) hybrid electrocatalyst for the hydrogen evolution reaction (HER). The O-MoS2 QDs were prepared with a one-pot microwave method by hydrazine-mediated oxygen-doping. The synthetic method is straightforward, time-saving, and can be applied in large scale preparation. Ultra-small O-MoS2 QDs with the average size of 5.83 nm and 1-4 layers can be uniformly distributed on the surface of reduced graphene oxide (RGO). Benefited from the unique structure and the doping effect of oxygen in the MoS2 QDs and the great number of active sites, the O-MoS2 QD hybrid displayed outstanding electrocatalytic performance toward HER. A low overpotential of 76 mV at 10 mA/cm2 and a Tafel slope of 58 mV/dec were obtained in an acidic solution toward HER. Additionally, the resultant O-MoS2 QD hybrid also exhibited excellent stability and durability toward HER, displaying negligible current density loss after 1000 cycles of cyclic voltammetry. The design and synthesis of the electrocatalyst in this work open up a prospective route to prepare active and stable electrocatalysts toward substituting precious metals for hydrogen generation.

In-situ transformation to accordion-like core-shell structured metal@metallic hydroxide nanosheet from nanorod morphology for overall water-splitting in alkaline media

Exploring highly-efficient, low-cost and earth-abundant bi-functional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have a key role in economical overall water-splitting. Herein, a facile and general route is developed to prepare various non-noble metal-based electrocatalysts via NH3⋅H2O treatment (NT) on Ni foam (NF) (M-NT/NF, M = Co, Ni, Fe, Mn, Cu). The morphology and compositions of the obtained catalysts could be tuned via solvothermal process with NH3⋅H2O, and then optimizing the active sites exposure and effectively change the reaction kinetics of the electrocatalytic reaction. Moreover, the substrate of Ni foam is in favor of electrolyte transfer and release of produced gases. Then, the obtain Co-NT/NF, composed of metallic Co and Co(OH)2, exhibits excellent catalytic performance for HER with low overpotential of 178 mV@10 mA cm−2 and small Tafel slope of 75 mV dec−1, which is rarely reported for HER. For OER, only a low overpotential of 226 mV is required to deliver 10 mA cm−2 with a small Tafel slope of 46 mV dec−1. Moreover, the reported electrocatalysts present negligible current density loss during long-term stability measurement, demonstrating robust nanostructure feature of the prepared catalysts. This work opens a facile and efficient avenue to design bi-funtional electrocatalyst coupling with outstanding catalytic performance.

Fe3O4 encapsulated in porous carbon nanobowls as efficient oxygen reduction reaction catalyst for Zn-air batteries

Zn-air batteries have received extensive attention because of their high energy density, environmental friendliness, low cost and safety. It is vital to develop cost-effective and stable electrocatalysts for oxygen reduction reaction for Zn-air batteries. Herein, Fe3O4 encapsulated in porous carbon nanobowls (Fe3O4@PCN) for oxygen reduction reaction are prepared by simple soft-template approach and calcination subsequently. The optimized catalyst 4Fe3O4@PCN-800 with uniformly doped Fe3O4 nanoparticles and large surface area exhibits excellent catalytic performance and long-term durability. It displays 66 mV higher half-wave potential (0.911 V) than that of 20 wt% Pt/C catalysts in 0.1 M KOH electrolyte. It also shows excellent durability, only 5 mV attenuation of halfwave potential after 10,000 potential cycles. In addition, 4Fe3O4@PCN-800 possesses better methanol resistance than Pt/C, negligible current density fluctuation in the basic electrolyte with 3 M methanol. Impressively, when being employed as a cathode catalyst in both aqueous and solid-state Zn-air batteries, 4Fe3O4@PCN-800 presents higher open-circuit voltage, higher capacity and peak power density, and more stable discharge voltage plateaus than those of Pt/C. Furthermore, the solid-state Zn-air batteries with the optimal synthesized catalyst exhibit encouraging flexibility, which have enormous potential in the application of flexible and wearable power sources.

Hydrophobic Polystyrene Passivation Layer for Simultaneously Improved Efficiency and Stability in Perovskite Solar Cells.

The major restraint for the commercialization of the high-performance hybrid metal halide perovskite solar cells is the long-term stability, especially at the infirm interface between the perovskite film and organic charge-transfer layer. Recently, engineering the interface between the perovskite and spiro-OMeTAD becomes an effective strategy to simultaneously improve the efficiency and stability in the perovskite solar cells. In this work, we demonstrated that introducing an interfacial polystyrene layer between the perovskite film and spiro-OMeTAD layer can effectively improve the perovskite solar cells photovoltaic performance. The inserted polystyrene layer can passivate the interface traps and defects effectively and decrease the nonradiative recombination, leading to enhanced photoluminescence intensity and carrier lifetime, without compromising the carrier extraction and transfer. Under the optimized condition, the perovskite solar cells with the polystyrene layer achieve an enhanced average power efficiency of about 19.61% (20.46% of the best efficiency) from about 17.63% with negligible current density-voltage hysteresis. Moreover, the optimized perovskite solar cells with the hydrophobic polystyrene layer can maintain about 85% initial efficiency after 2 months storage in open air conditions without encapsulation.

Nickel-Incorporated, Nitrogen-Doped Graphene Nanoribbons as Efficient Electrocatalysts for Oxygen Evolution Reaction

We report a scalable method for the preparation of nickel incorporated nitrogen-doped graphene nanoribbon (Ni/NGNRs) through a facile solvothermal process. Significantly, we show that the incorporation of nitrogen functionalities on graphene nanoribbon with tunable nickel content not only catalyzes efficiently the water oxidation reaction but enables to tweak the catalytic reactivity. Thus, Ni/NGNRs composite with higher nickel content exhibits an overpotential of 380 mV with a Tafel slope of 60 mV dec−1 to sustain 10 mA cm−2 under alkaline conditions. Furthermore, only a negligible current density drop is witnessed during the chronoamperometric studies suggesting the robust nature of the electrocatalyst. XPS analysis of the composite before and after polarization studies confirms the formation of nickel oxide on the exposed nickel nanoparticles during the electrochemical reaction but without any major adverse effect on the performance. We attribute the formation of nickel oxide on the exposed nickel nanoparticles as the major reason for the observed enhancement of electrocatalytic performance.

Pseudohalide‐Induced Recrystallization Engineering for CH3NH3PbI3 Film and Its Application in Highly Efficient Inverted Planar Heterojunction Perovskite Solar Cells

AbstractHigh crystallinity and compactness of the active layer is essential for metal‐halide perovskite solar cells. Here, a simple pseudohalide‐induced film retreatment technology is developed as the passivation for preformed perovskite film. It is found that the retreatment process yields a controllable decomposition‐to‐recrystallization evolution of the perovskite film. Corresponding, it remarkably enlarges the grain size of the film in all directions, as well as improving the crystallinity and hindering the trap density. Meanwhile, owing to an intermediate catalytic effect of the pseudohalide compound (NH4SCN), no crystal orientation changing and no impurity introduction in the modified film. By integrating the modified perovskite film into the planar heterojunction solar cells, a champion power conversion efficiency of 19.44% with a stabilized output efficiency of 19.02% under 1 sun illumination is obtained, exhibiting a negligible current density–voltage hysteresis. Moreover, such a facile and low‐temperature film retreatment approach guarantees the application in flexible devices, showing a best power conversion efficiency of 17.04%.

High‐Performance Inverted Planar Heterojunction Perovskite Solar Cells Based on Lead Acetate Precursor with Efficiency Exceeding 18%

Organic–inorganic lead halide perovskites are emerging materials for the next‐generation photovoltaics. Lead halides are the most commonly used lead precursors for perovskite active layers. Recently, lead acetate (Pb(Ac)2) has shown its superiority as the potential replacement for traditional lead halides. Here, we demonstrate a strategy to improve the efficiency for the perovskite solar cell based on lead acetate precursor. We utilized methylammonium bromide as an additive in the Pb(Ac)2 and methylammonium iodide precursor solution, resulting in uniform, compact and pinhole‐free perovskite films. We observed enhanced charge carrier extraction between the perovskite layer and charge collection layers and delivered a champion power conversion efficiency of 18.3% with a stabilized output efficiency of 17.6% at the maximum power point. The optimized devices also exhibited negligible current density–voltage (J–V) hysteresis under the scanning conditions.

Effective bioelectrocatalysis of bilirubin oxidase on electrochemically reduced graphene oxide

Graphene oxide (GO) was applied for construction of an effective biocathode based on bilirubin oxidase (BOD). Separation of small-sized GO sheets together with the BOD immobilisation protocol has detrimental effects on the bioelectrocatalytic reduction of oxygen. When BOD was deposited on electrochemically reduced GO (ErGO) only a negligible current density j=2.6μAcm−2 was observed. Current density dramatically increased to a value of 46μAcm−2 once BOD was in-situ mixed with as-received GO directly on a glassy carbon electrode (GCE) with subsequent electrochemical reduction of the BOD/GO composite. When this protocol was tested with small-sized GO flakes separated simply using centrifugation, the fabricated biocathode exhibited j=120μAcm−2. A current density further increased to j=280μAcm−2 when BOD and purified GO were incubated ex-situ for 4h, followed by the BOD/GO composite collection by centrifugation, its deposition on the GCE and electrochemical reduction. Moreover, oxygen reduction current increased steeply with a steady-state current density achieved at high potential (≈500mV), close to the onset potential of oxygen reduction (≈580mV).