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Water electrolysis is an efficient approach for high-purity hydrogen production. However, the anodic sluggish oxygen evolution reaction (OER) always needs high overpotential and thus brings about superfluous electricity cost of water electrolysis. Therefore, exploiting highly efficient OER electrocatalysts with small overpotential especially at high current density will undoubtedly boost the development of industrial water electrolysis. Herein, we used a simple hydrothermal method to prepare a novel FeOOH–CoS nanocomposite on nickel foam (NF). The as-prepared FeOOH–CoS/NF catalyst displays an excellent OER performance with extremely low overpotentials of 306 and 329 mV at 500 and 1000 mA cm−2 in 1.0 M KOH, respectively. In addition, the FeOOH–CoS/NF catalyst can maintain excellent catalytic stability for more than 50 h, and the OER catalytic activity shows almost no attenuation no matter after 1000 repeated CV cycles or 50 h of stability test. The high catalytic activity and stability have exceeded most non-noble metal electrocatalysts reported in literature, which makes the FeOOH–CoS/NF composite catalyst have promising applications in the industrial water electrolysis.

Low-temperature industrial water electrolysis is typically conducted using either liquid alkaline electrolytes or acidic polymer electrolyte membranes (PEMs). The latter approach is considered to be more efficient but also more expensive as it requires Pt and Ir based catalysts. This study reports on an alkaline water electrolyzer with Ni electrodes that operates at a current density of 2 A/cm2 with a cell voltage of 1.85 V, which provides a comparable voltage-current characteristic to the state-of-the-art PEM water electrolyzers. Thin Ni mesh electrodes with surface areas that are thousand times higher than the geometric area were manufactured by an easily scalable and cheap process, i.e. metallurgical hot dip galvanization with subsequent de-alloying. With a thin porous polymer of approximately 140 μm as the diaphragm a low cell resistance of 0.11 Ω cm−2 was obtained.

This study presents a novel structure of catalyst layers of membrane electrode assemblies (MEAs) by adding graphene to platinum on carbon black (Pt/C) to improve the durability at high current density operation (3 A cm−2). Graphene displays outstanding low electrical resistance and has the advantage of high electron mobility. It is also used in lithium ion batteries to improve electrical performance such as high rate charge/discharge capability and cycle-life stability. In this study, three MEAs are compared, and graphene is used as an excellent conductive additive in catalyst layers for better electrons transport at high current density operation. The MEA coated Pt/C mixed with 0.1 wt% graphene shows best durability for 0.3 V h−1 which is almost 3.7 times better than that of without graphene additive (1.1 V h−1). The graphene additive effectively extends the durability of the MEA. Furthermore, the MEAs are analyzed by AC impedance. The impedance arc of the MEA coated with Pt/C only is getting worse, but those two coated with graphene show similar and smaller impedance arcs after high current density operation for 80 h.

This paper deals with the development work in Bhabha Atomic Research Centre, India, on alkaline water electrolysis cells. Indigenous development of an advanced type, high amperage, high pressure electrolyser using porous nickel electrodes for tonnage production of hydrogen is described. Methods of producing porous nickel plaques and other cell components are also presented. Operation and performance characteristics of the cells are reported.

To investigate the effectiveness of a novel compound flow field design concerned in PEM fuel cell, computational fluid dynamics (CFD) approach is employed. A novel compound flow field design along with typical serpentine and parallel designs is verified through three dimensional simulations. The numerical results for different reactant flow fields yield to observation of parameters like current density, membrane mass fraction of water and etc. Comparison of the results revealed that the way reactants are distributed on the surface is substantial. Driving the polarization curve for the three flow fields, it is seen that the parallel flow field demonstrated weaker performance in comparison to the other two models. The main reason is associated to insufficient distribution of the reactants. Analyzing the polarization curve of the compound design along with other contours it can be said that this design can be a good candidate for preventing the flooding phenomena while its performance is approximately the same as the serpentine type. So employment of the so-called design can be strongly recommended for high current density operating condition.

This study correlates the post start cell performance and impedance with the cold start process in the subzero environment. The sequential failed cold starts are deliberately conducted as well as the start at small current density. Here the failed cold start means the cell voltage drops to or below zero within very short time during the start process. It is found that there are reversible performance losses for the sequential failed cold starts, while not obvious degradation and no recovery happen for the start at small current density. Using the thin film and agglomerate model, it is confirmed that this is due to the water blocking effect. Comparing the results from different start processes, a model with respect to the shifting of reactive region within the catalyst layer is applied to explain that the reversible performance loss is associated with the amount of the generated water or ice and the water location or distribution during cold start. The relationship of the cold start performance at high current density and the pore volume in the catalyst layer is also discussed.

Besides developing a large number of catalysts for hydrogen evolution reaction (HER) in alkaline electrolytes, its conversion efficiency remained low. Herein, we have developed mixed-dimensional heterostructures of niobium disulfide (NbS2) with graphene foam grown on nickel foam (NbS2-Gr-NF). The strong lateral fusion results in activating the catalytic sites of NbS2, the three-dimensional substrate provides easy access of electrolyte to active sites and increased electrochemically active surface area, while enhanced conductivity provides faster transfer of electrons to and from active sites. Therefore, NbS2-Gr-NF heterostructures resulted in an exceptionally high current density of 500 mA cm−2 at a very low overpotential of 306 mV in 1 M KOH solution and even can achieve the current density values of 914 mAcm−2 at 338 mV only at a slight increase in overpotential (32 mV). Moreover, a Tafel value of ~72 mV dec−1 confirms that as-developed heterostructure provides fast reaction kinetics where the reaction is mainly controlled by the Volmer step. Achieving such high current density at a faster rate with high stability makes NbS2-Gr-NF heterostructures a potential candidate for water-splitting, especially in alkaline electrolytes.

The rib size is a critical engineering design parameter for high temperature proton exchange membrane fuel cell (HT-PEMFC) stack development, yet it hasn't been studied for HT-PEMFC. A three-dimensional, non-isothermal model was developed in this work to investigate the effect of channel to rib width ratios (CRWR) on the performance of HT-PEMFC. The reaction heat caused by entropy change was divided into cathodic half-reaction heat and anodic half-reaction heat. The results show that the ratio value significantly influence the gas diffusion, electron conduction and the distribution of current density in the porous electrodes. Increasing this ratio facilitates gas transport in the porous electrode but causes higher ohmic loss due to longer distance for electron conduction. As a result, an optimal ratio of about 1 is observed, which results in a peak power density of 0.428 W/cm2. High current density is observed under the channel with a small ratio value while a high ratio value would cause high current density to appear under the rib, signifying the rib size effect on electrochemical behavior of HT-PEMFC. Apart from the electrical power output, the CRWR value also greatly influences the fluid flow and temperature distribution inside the cell, which would influence the long-term stability of HT-PEMFC. In the subsequent studies, efforts will be made to develop new stack configurations with more uniform gas distribution, short electron conduction path and low temperature gradient.

The rational design of non-precious-metal bifunctional catalysts of oxygen and hydrogen evolution reactions that generate a high current density and stability at low over potentials is of great significance in the field of water electrolysis. Herein, we report a facile and controllable method for the in-situ growth of urchin-like FeOOH–NiOOH catalyst on Ni foam (FeOOH–NiOOH/NF). X-ray photoelectron spectroscopy confirms that the proportion of Ni and Fe species with high valence state gradually increase with the extension of growth time. Electrochemical studies have shown that the optimized FeOOH–NiOOH/NF-24 h and −12 h catalysts demonstrate excellent electrochemical activity and stability in oxygen/hydrogen evolution reactions. Moreover, the cell voltage is reduced around 0.15 V at high current density (0.5–1.0 A cm−2) as compared to the state-of the art RuO2/NF(+)||Pt–C/NF(−) system, far better than most of the previously reported catalysts. The cost analyst revealed that using FeOOH–NiOOH/NF catalyst as both electrodes could potentially reduce the price of H2 around 7% compared with traditional industrial electrolyzers. These excellent electrocatalytic properties can be attributed to the unique urchin-like structure and the synergy between Ni and Fe species, which can not only provide more active sites and accelerate electron transfer, but also promote electrolyte transport and gas emission.

In this work the thermal limitations of high current density proton exchange membrane water electrolysis are investigated by the use of a one dimensional model. The model encompasses in-cell heat transport from the membrane electrode assembly to the flow field channels. It is validated by in-situ temperature measurements using thin bare wire thermocouples integrated into the membrane electrode assemblies based on Nafion® 117 membranes in a 5 cm2 cell setup. Heat conductivities of the porous transport layers, titanium sinter metal and carbon paper, between membrane electrode assembly and flow fields are measured in the relevant operating temperature range of 40 °C – 90 °C for application in the model. Additionally, high current density experiments up to 25 A/cm2 are conducted with Nafion® 117, Nafion® 212 and Nafion® XL based membrane electrode assemblies. Experimental results are in agreement with the heat transport model. It is shown that for anode-only water circulation, water flows around 25 ml/(min cm2) are necessary for an effective heat removal in steady state operation at 10 A/cm2, 80 °C water inlet temperature and 90 °C maximum membrane electrode assembly temperature. The measured cell voltage at this current density is 2,05 V which corresponds to a cell efficiency of 61 % based on lower heating value. Operation at these high current densities results in three to ten-fold higher power density compared to current state of the art proton exchange membrane water electrolysers. This would drastically lower the material usage and the capital expenditures for the electrolysis cell stack.

The porous transport layer (PTL) in polymer electrolyte membrane water electrolysers (PEMWEs) has the multiple roles of delivering water to the electro-catalyst, removal of product gas, and acts as a conduit for electronic and thermal transport. They are, thus, a critical component for optimized performance, especially at high current density operation. This study examines the relationship between the microstructure and corresponding electrochemical performance of commonly used titanium sinter PTLs. Four PTLs, with mean pore diameter (MPD) ranging from 16 μm to 90 μm, were characterized ex-situ using scanning electron microscopy and X-ray computed micro-tomography to determine key structural properties. The performance of these PTLs was studied operando using polarization and electrochemical impedance spectroscopy. Results showed that an increase in mean pore size of the PTLs correlates to an increase in the spread and multimodality of the pore size distribution and a reduction in homogeneity of porosity distribution. Electrochemical measurements reveal a strong correlation of mean pore size of the PTLs with performance. Smaller pore PTLs showed lower Ohmic resistance but higher mass transport resistance at high current density of 3.0 A cm−2. A non-monotonic trend of mass transport resistance was observed for different PTLs, which suggests an optimal pore size beyond which the advantageous influence of macroporosity for mass transport is diminished. The results indicate that maximizing contact points between the PTL and the catalyst layer is the overriding factor in determining the overall performance. These results guide PTL design and fabrication of PEMWEs.

A novel one step method was developed to dope nitrogen (N), sulfur (S) and carbon (C) in the Fe nanoparticles-dispersed carbon nanofibers (CNFs) grown over carbide-derived carbon (CDC), using thiourea as the single source of N, S and C. The synthesized N/S-Fe-CNF/CDC electrode was successfully used in a microbial fuel cell (MFC). When tested as the oxygen reduction reaction (ORR) catalyst, the electrode achieved a high current density (2.261 ± 0.002 mA/cm2), high OCP (0.611 ± 0.005 V), high stability upto 400 cycles, response time of ∼11 s, electron transfer number in the range 3.73–4.03, and Tafel slopes of −0.0627 and −0.183 V/dec at low and high current densities, respectively. A first order kinetics and a 4e− pathway were deduced from the ORR analysis. Notably, the fabricated MFC based on the prepared electrode produced a high current density of 1.3887 ± 0.002 mA/cm2, high OCP of 0.626 ± 0.005 V and maximum power density of 0.238 ± 0.002 mW/cm2, attributed to the synergistic effects of heteroatoms, Fe nanoparticles, and CNFs.

The performance of polymer electrolyte membrane (PEM) fuel cells highly depends on their mass transport property at high current density operation. To improve the mass transport property, various types of flow-fields have been developed, such as serpentine, straight, grid, and porous flow-fields. Because of the limits of thin land and channel width, the authors have developed a porous type flow-field with unique pore diameter distribution. Unlike general types of porous flow-fields, it has a double peak in the pore diameter distribution; in this paper, it is called a “bi-porous flow-field”. The structure was intended to have organized flow paths for liquid water and gas. The paper investigates its performance and impedance characteristics compared with those of the conventional flow fields. The results of the analysis on the polarization and electrochemical impedance spectrometry revealed that the bi-porous flow-field exhibits the smallest gas diffusion resistance at a high current density operation regardless of humidity conditions. These results indicate that the bi-porous flow-field conducts water management well at high current density. In low humidity conditions, however, dry-out tends to occur and must be prevented.

To improve cell performance, the effects of heat treatment time on the electrochemical properties and electrode structure of PTFE-bonded membrane electrode assemblies for PBI-based high-temperature proton exchange membrane fuel cells are investigated. The cell performance is observed to decrease in the high-current-density region rather than in the low-current-density region with increasing heat treatment time at 350 °C from 1 to 30 min. Microscopic studies reveal remarkable differences in the electrode structure by the agglomeration of dispersed PTFE and adjacent catalyst particles, depending on the heat treatment time. As the heat treatment time increases, only the large pore (secondary pore) volume in the electrode decreases, resulting in increase in mass transport resistance and concentration overpotential in the high-current-density region. Cell performance is not measured without heat treatment because the electrodes are not formed. When the electrodes are heat treated for 1 min at 350 °C, the best cell performance is obtained, 0.67 V at 200 mA cm −2 .

Rapid degradation phenomenon is generally occurred when Ni-based anode on a cathode-supported SOFC is operated in low concentrations of hydrogen at high current density. In order to clarify this phenomenon, homogenous NiO-Ce0.8Gd0.2O1.9 (CGO) composites powder with fixed weight ratio of Ni:Ce was synthesized using a nitric-citrate sol-gel method, and coated on LSM-CGO cathode-supported SOFC using slurry coating method. As-prepared fuel cells exhibited good performance when they were operated at pure H2. However, rapid degradation phenomenon on Ni-CGO anode usually happened when low concentration of H2 was used as fuel at high current density. Obvious microstructure damage and sintering of Ni were observed in SEM micrographs of Ni-CGO anode after repeated degradation process in 5.66% of H2 at high current density. Furthermore, the decrease in Ni amount in Ni-CGO anode was also found via EDX analysis when this degradation process was repeated for several times. It is inferred that the volatilization of nickel hydroxide should happen at triple-phase boundaries of Ni-CGO anode when high partial pressure ratio of H2O and H2 appeared in this case.

An ongoing challenge still lies in the exploration of proficient electrocatalysts from earth-abundant non-precious metals instead of noble metal-based catalysts for clean hydrogen energy through large-Scale electrochemical water splitting. However, developing a non-precious transition metals based, stable electrocatalyst for cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) is important challenge for modern energy conversion technology. In this report Vanadium doped bimetallic nickel-iron nanoarray, fabricated by carbon supported architecture through carbonization process for electrochemical water splitting. Three types of catalysts were prepared in different molar ratio of Ni/Fe. The electrocatalytic performance demonstrated that the catalyst with equal mole ratio (0.06:0.06) of Ni/Fe possess high catalytic activity for both OER and HER in alkaline and acidic medium. Besides, our findings revealed that the doping of vanadium could play a strong synergetic effect with Ni/Fe, which provide a small overpotential of 90 mV and 210 mV at 10 mA cm−2 for HER and OER respectively compared to the other two catalyst counterparts. Also, the catalyst with 1:1 (Ni/Fe) molar ratio showed a high current density of 208 mA cm−2 for HER at 0.5 M H2SO4 and 579 mA cm−2 for OER at 1 M KOH solution, the both current densities are much higher than the other two catalysts (different Ni/Fe ratio). In addition, the presented catalysts showed extremely good durability, reflecting in more than 20 h of consistent Chronoamprometry study at fixed overpotential η = 250 mV without any visible voltage elevation. Similarly, the (Ni/Fe) equal ratio catalyst showed better corrosion potential 0.209 V vs Ag/AgCl and lower current density 0.594 × 10−12 A cm−2 in high alkaline medium. The V-doping, MOF/GO surface defects are significantly increased the corrosion potential of the V-NixFey-MOF/GO electrocatalyst. Besides, the water electrolyzed products were analysed by gas chromatography to get clear insights on the formed H2 and O2 products.

Although many studies have been done on finding operating conditions of hydrogen-fed fuel cells before, it remains one of the most critical points in determining its parameters in the process. So this paper aims to investigate experimentally the reactant gases flow rate and cell voltage which have a significant impact on the current density of a 3-cell Proton Exchange Membrane fuel cell stack having a 150 cm2 active layer. In this case, to determine the optimum values, Design of Experiment and Response Surface Methodology was applied to the experimental system at low 1.5 V, medium 1.8 V, and high 2.1 V. Then, they were compared with each other. In this context, keeping the hydrogen flow rate low and obtaining high current density is one of the main targets; at low voltage values, it was concluded that the flow rate should be increased due to the reaction rate increases with temperature. In general, the effect of humidification and cell temperature on performance was seen more prominently at 1.8 V. The highest current density values that were 313.66 mA/cm2, 336.75 mA/cm2, and 323.48 mA/cm2, respectively, were reached at flow rates of 1 L/min,1.3 L/min,1.6 L/min.

The multicomponent electrocatalyst is a low-cost composite material exhibiting excellent catalytic activity suitable for methanol oxidation reactions (MOR). In this work, we report a glassy carbon electrode modified nickel oxide nanospheres (NiO) decorated biomass-derived activated carbon (AC) nanosheets and polypyrrole (PPy) nanowire, electrocatalyst (NiO_AC@PPy/GCE) for direct methanol oxidation fuel cell (DMFC) application. The SEM micrographs reveal the nanosheets and nanowire-like morphology of AC and PPy decorated with NiO nanospheres which provide a high surface area with electrocatalytic activity, and stability for MOR. The NiO_AC@PPy/GCE exhibits a high current density of 551 mA/mg at a low onset potential of 0.5 V (vs Ag|AgCl) towards electro-oxidation of 0.5 M methanol (MeOH) in an alkaline medium. This superior performance of the NiO_AC@PPy/GCE over other reported metal-oxides based electrocatalysts is attributed to the synergistic effect of the NiO_AC@PPy electrocatalyst, wherein NiO provides electrocatalytic active sites for MOR via Ni2+/Ni3+ redox couple while the PPy and AC contribute towards the chemical stability and electrical conductivity of the electrode, respectively. The electrode shows 79% of capacity retention after 10,000 s of chronoamperometry displaying excellent chemical stability with reduced effect of CO intermediate poisoning at the electrode surface. This excellent stability and overall performance of the NiO_AC@PPy proves it as an ideal, low-cost non-noble electrocatalyst for DMFCs.

Enhancing mass transfer capability of flow channel is important subject to improve fuel cell performance. In this study, an experimental study about non-uniform arrangement of metallic structures in cathodic flow channel on polymer electrolyte membrane fuel cell is conducted. Metallic 3D printer is used to manufacture 3D mesh with complex geometry. Channel width and bottom-rear channel depth are selected to change the geometry of structure. Assuming that accelerating flow velocity and reinforcing flow direction to gas diffusion layer can improve fuel cell performance, eight basic arrangements are inserted into cathodic carbon bipolar plate to measure fuel cell performance. With I–V curve, the unit cells with non-uniform arrangements of width and tapered structure show performance enhancement of 12.8% in maximum power density, compared with conventional parallel flow channel. According to electrochemical impedance spectroscopy results, performance enhancement by non-uniform arrangement is mainly occur in high current density operation due to low mass transfer resistance.

It is an inevitable choice to find efficient and economically-friendly electrocatalysts to reduce the high overpotential of oxygen evolution reaction (OER), which is the key to improve the energy conversion efficiency of water splitting. Herein, we synthesized Cu2S/Ni3S2 catalysts on nickel foam (NF) with different molar ratios of Ni/Cu by a simple two-step hydrothermal method. Cu2S/Ni3S2-0.5@NF (CS/NS-0.5@NF) effectively reduces the overpotential of OER, displaying small overpotentials (237 mV@100 mA cm−2 and 280 mV@500 mA cm−2) in an alkaline solution, along with a low Tafel slope of 44 mV dec−1. CS/NS-0.5@NF also presents an excellent durability at a relatively high current density of 100 mA cm−2 for 100 h. The excellent performance is benefited by the prominent structural advantages and desirable compositions. The nanosheet has a high electrochemical active surface area and the porous structure is conducive to electrolyte penetration and product release. This work provides an economically-friendly Cu-based sulfide catalyst for effective electrosynthesis of OER.

Binder-free NiFe-based electrocatalyst with aligned pore channels has been prepared by freeze casting and served as a bifunctional catalytic electrode for oxygen and hydrogen evolution reaction (OER and HER). The synergistic effects between Ni and Fe result in the high electrocatalytic performance of porous NiFe electrodes. In 1.0 M KOH, porous Ni7Fe3 attains 100 mA cm−2 at an overpotential of 388 mV with a Tafel slope of 35.8 mV dec−1 for OER, and porous Ni9Fe1 exhibits a low overpotential of 347 mV at 100 mA cm−2 with a Tafel slope of 121.0 mV dec−1 for HER. The Ni9Fe1//Ni9Fe1 requires a low cell voltage of 1.69 V to deliver 10 mA cm−2 current density for overall water splitting. The excellent durability at a high current density of porous NiFe electrodes has been confirmed during OER, HER and overall water splitting. The fine electrocatalytic performances of the porous NiFe-based electrodes owing to the three-dimensionally well-connected scaffolds, aligned pore channels, and bimetallic synergy, offering excellent charge/ion transfer efficiency and sizeable active surface area. Freeze casting can be applied to design and synthesize various three-dimensionally porous non-precious metal-based electrocatalysts with controllable multiphase for energy conversion and storage.

Bimetallic Ni–Fe phosphide electrocatalysts were in-situ synthesized through direct phosphorization of metal salts on carbon cloth (CC). The Fe dopant remarkably enhances the OER performance of Ni2P in alkaline medium through the electronic structure modulation of Ni. The (Fe0.5Ni0.5)2P/CC electrode, composed of uniform films coated on carbon fibers, delivers a low overpotential of 260 mV with a small Tafel slope of 45 mV·dec−1 at the current density of 100 mA cm−2, outperforming most reported non-noble electrocatalysts and commercial RuO2 electrocatalyst. The (Fe0.5Ni0.5)2P/CC also displays superior electrochemical stability at high current density. An appropriate Fe dopant level facilitates the in-situ transformation of Ni–Fe phosphides into active NiFeOOH during alkaline OER. This work simplifies the synthesis procedure of metal phosphides.

UVC (ultrathin vapor chamber) simultaneously has a high heat-conducting property, excellent temperature uniformity and simple structure. These advantages are very suitable for thermal management of the open-cathode PEMFC (proton exchange membrane fuel cell) stack. In this work, two-type UVCs with different appearances are integrated into a conventional PEMFC stack respectively. The effect of UVC on the output performance, thermal management and operating stability is investigated by the experiment combined with simulation. The results show that UVC can significantly increase the output voltage under high current density. In 35 A, the output voltage of the stack integrated the vertical UVC increases by 20.25% relative to the conventional stack. Thermal management is also improved by UVC. The highest temperature inside the stack decrease by 9 °C in 35 A, and the membrane temperature is decreased obviously. But it still exceeds the optimal operating temperature of open-cathode PEMFC stack due to the poor cooling type in the condensation side of UVC. UVC improves the operation stability of the stack and slows the deteriorative speed of output performance. This work hopes to attract more attention to the application of UVC on the thermal management of portable power sources used open-cathode PEMFC stack.

Polymer electrolyte membrane (PEM) fuel cell technology needs to overcome the cost barrier in order to compete with the internal combustion engines (ICEs) for transportation application. A viable approach is to raise fuel cell's power output without increasing its size and Pt loading in the catalyst layers (CLs). In this strategy, the cost per kW power output can be proportionally reduced due to the increased power density. This paper examines this strategy by exploring several important aspects that influence fuel cell performance under high power or current density using a three-dimensional (3-D) fuel cell model. It is shown that local CLs may be subject to low oxygen concentration under a high current density of 2 A/cm2, causing low reaction rate near the outlet, especially under the land. Additionally, the oxygen reduction reaction (ORR) rate may be subject to a large through-plane variation under 2 A/cm2, raising ohmic voltage loss in the CL. Two additional cases are investigated to improve fuel cell performance under 2 A/cm2: one has a 5 times thinner CL with the same ORR kinetics per membrane electrode assembly (MEA) area and the other has a 5 times thinner CL with 5 times higher ORR kinetics. The results show the output voltage is raised approximately from 0.5 V to 0.554 V in the former CL case and further to 0.606 V for the latter CL. To enable high-efficiency operation (e.g. >50%), thinner CLs with high ORR kinetics and GDLs with better transport properties are one research and development (R&D) direction.

Alkaline water electrolysis has the advantage of scalability for industrial-scale mass production of hydrogen; however, it is operated under a lower current density than other methods of water electrolysis because a high overpotential resulting from ion transport limitations will occur at high current density. Bubble dynamics can both prevent ion transport by its existence and accelerate it by bubble-induced flow. In this study, we conduct three-dimensional coupling numerical simulations of two-phase flow and electrochemical phenomena to elucidate the mechanisms by which microscale bubble dynamics influence ion transport and the cell overpotential. We find that the flow induced by rising microbubbles enhances ion transport to the anode and suppresses the cell overpotential. Moreover, bubble atomization further suppresses the overpotential because smaller bubbles approach the anode more closely than larger ones and accelerate ion transport to the anode surface.

The exploration of efficient catalysts toward hydrogen evolution reaction (HER) is still an urgent task. In this paper, Ni/Mo/Cu/C and Ni/Mo/C electrode were obtained by conventional pulse voltammetry, which acted as cathode in microbial electrolysis cells (MECs). The prepared samples are analyzed using SEM, XRD, XPS and electrochemical analysis techniques. Results indicated that the Ni/Mo/Cu coating has a rough and globular structure and presents high current density, a lower Tafel slope of 23.9 mV/dec than 30 mV/dec of Pt, which exceeds the electrochemical activity of Pt electrode. Its remarkably enhanced electrocatalytic activity is attributed to the high surface area, high conductivity as well as synergistic interaction among Ni, Mo and Cu.

The production of hydrogen, a favourable alternative to an unsustainable fossil fuel remains as a significant hurdle with the pertaining challenge in the design of proficient, highly productive and sustainable electrocatalyst for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, the dysprosium (Dy) doped copper oxide (Cu1-xDyxO) nanoparticles were synthesized via solution combustion technique and utilized as a non-noble metal based bi-functional electrocatalyst for overall water splitting. Due to the improved surface to volume ratio and conductivity, the optimized Cu1-xDyxO (x = 0.01, 0.02) electrocatalysts exhibited impressive HER and OER performance respectively in 1 M KOH delivering a current density of 10 mAcm−2 at a potential of −0.18 V vs RHE for HER and 1.53 V vs RHE for OER. Moreover, the Dy doped CuO electrocatalyst used as a bi-functional catalyst for overall water splitting achieved a potential of 1.56 V at a current density 10 mAcm−2 and relatively high current density of 66 mAcm−2 at a peak potential of 2 V. A long term stability of 24 h was achieved for a cell voltage of 2.2 V at a constant current density of 30 mAcm−2 with only 10% of the initial current loss. This showcases the accumulative opportunity of dysprosium as a dopant in CuO nanoparticles for fabricating a highly effective and low-cost bi-functional electrocatalyst for overall water splitting.

In the present study, a novel electrocatalyst with excellent catalytic performance based on PdCu bimetallic nanoparticles (NPs) supported on ordered mesoporous silica and multi-walled carbon nanotubes (PdCu NPs/SBA-15-MWCNT) was prepared for electrochemical hydrogen evolution reaction (HER). For this purpose, low-cost mesoporous SBA-15 was synthesized using silica extracted from Stem Sweep Ash (SSA) as an economically attractive silica source. Mesoporous SBA-15 with unparalleled porous structure is a stable support for PdCu bimetallic NPs which prevents the accumulation of PdCu bimetallic NPs and improves its efficiency in the catalytic process. The main advantage of this strategy is low loading of bimetallic catalyst with high catalytic activity. The presence of both mesoporous SBA-15 and MWCNTs materials in PdCu/SBA15-MWCNTs/carbon paste electrode (CPE) increases the metallic active sites and the electrical conductivity of electrode which provides great performance for HER. PdCu/SBA15-MWCNTs-CPE provided small Tafel slope (45 mV dec−1), low onset potential (~-150 mV), high current density (−165.24 mA cm−2at -360 mV) and exchange current density (2.51 mA cm−2) with great durability for HER in H2SO4 solution. Analysis of kinetic data suggests that the electrocatalyst controls HER by the Volmer-Heyrovsky mechanism. In addition, studies showed that the presence of sodium dodecyl sulfate (SDS) in electrolyte can decrease the potential of HER and increase the current density.

The creation of carbon matrices with a high surface area for effective catalytic activity is an urgent task today, especially in the field of electrocatalysis. In this study, microporous carbon (MPS) with a surface area of about 1300 m2 g−1 was produced from raw plant waste (apricot pit shells) by successive thermal carbonation and chemical treatment. The MPS was impregnated with H2PdCl6 and calcined at various temperatures under a H2–Ar flux. The obtained Pd-NP@MPC (nanoparticle size from 1 to 25 nm) catalysts were characterized in detail by XRD, SEM, TEM and BET methods. Electrochemical tests show that the prepared composites exhibit high electrocatalytic activity and remarkable stability over time (over 50 h) for the HER process and overall water splitting performance. The electrodes have very low overpotentials (η) of 95–117 mV for HER in 1 M KOH at a current density of 100 mA cm−2. Furthermore, the Pd-NP@MPC-300 electrode can reach a high current density of 300 mA cm−2 at η merely of 170 mV and shows excellent electrocatalytic stability in prolonged water electrolysis. The relationships between MPC matrix characteristics, Pd NPs size and electrocatalytic properties are discussed in this paper.

Electrochemical reactions such as the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and methanol oxidation reaction (MOR) are essential for energy conversion applications such as water electrolysis and fuel cells. Furthermore, Pt or Ir-related materials have been extensively utilized as electrocatalysts for the OER, ORR, and MOR. To reduce the utilization of precious metals, innovative catalyst structures should be proposed. Herein, we report a bi-metallic phosphide (Ni2P and PdP2) structure surrounded by graphitic carbon (Ni–Pd–P/C) with an enhanced electrochemical activity as compared to conventional electrocatalysts. Despite the low Pd content of 3 at%, Ni–Pd–P/C exhibits a low overpotential of 330 mV at 10 mA cm−2 in the OER, high specific activity (2.82 mA cm−2 at 0.8 V) for the ORR, and a high current density of 1.101 A mg−1 for the MOR. The superior electrochemical performance of Ni–Pd–P/C may be attributed to the synergistic effect of the bi-metallic phosphide structure and core-shell structure formed by graphitic carbon.

To solve the issues of energy shortage and environmental pollution, it is essential to develop highly effective catalysts for hydrogen evolution reaction (HER) in water electrolysis. Herein, we report a facile and rapid fabrication of a Cu–Co–P catalyst on a carbon paper (CP) substrate using electrodeposition. First, the deposition conditions for Co–P/CP were optimized. The prepared Co–P consisted of numerous spheres and exhibited acceptable catalytic activity towards HER in an alkaline medium with an overpotential of 72 mV at current density of −10 mA/cm2. Further performance enhancement was achieved by the incorporation of Cu to modify the electronic structure of the Co–P catalyst. In a half-cell test, the optimized Cu–Co–P/CP exhibits remarkable performance, achieving −10 mA/cm2 at an overpotential of 59 mV, and the Tafel slope is 38 mV/dec. In a single-cell test, an anion exchange membrane water electrolyzer with a Cu–Co–P/CP cathode and commercial IrO2/CP anode exhibited high current density of 0.70 A/cm2 at 1.9 Vcell.

Hydrogen used as an energy carrier can be obtained by water electrolysis. To improve the energy efficiency of this process porous nickel catalysts are often used. The paper investigates the electrodeposition regularities and the porous nickel deposits morphology and the properties of nickel foams toward the hydrogen evolution reaction. During electrodeposition at high current density, nickel deposits with macro- and micropores are formed. The dependence between the fraction of macropores on the deposit surface and the electrolysis time is described by the empirical equation. Total porosity of loose nickel deposits is much higher than the porosity of foams. However, the surface macropores fraction of deposits studied is approximately the same, while the microporosity of loose deposits is significantly higher. The values of nickel deposits total porosity calculated by the model agree with the values obtained by experimental data. The highest density of macropores on the surface is observed for the foam thickness of 100 μm. These data correlate with the results of polarization measurements. When the foam thickness increases up to 100 μm, hydrogen evolution overvoltage in the alkali solution decreases and the efficiency of nickel foam as a cathode material increases.

Solvothermal Bi2MoO6 hierarchical microflowers synthesis has been successfully attempted. Methanol, ethanol and isopropanol have been mediated to synthesize three kinds of Bi2MoO6 hierarchical microflowers. Highly oriented (311) plane growth of orthorhombic Bi2MoO6 hierarchical microflowers have been confirmed. Interstitial vacancies and its role on electrochemical activity have been extensively discussed. Electrode fabrication was constructively done by using Ni foam substrate. Half cell arrangement of each electrode in alkaline medium has been designed to measure the electrochemical activity towards water oxidation. High current density of 356 mA/cm2 was afforded by Bi2MoO6 hierarchical microflowers mediated by ethanol solvent during synthesis. Low Tafel slope value of 43 mV/dec has been reported to obtain 10 mA/cm2 current density. Higher conductivity long with very good electron transportation has been achieved and is also adapted for 12 h long time stability test and achieved 86% of retention in its performance. Hence, optimally prepared Bi2MoO6 hierarchical microflowers could be an efficient electrode for clean energy fabrication.

In this study, nickel cobalt oxide (NiCo2O4) microspheres were prepared by using facile hydrothermal route. The structural confirmation of bimetal oxide formation was acquired by X-ray powder diffraction and Raman studies. The formation of microspheres combined via irregular nanosheets was confirmed by scanning electron microscopy. Highly oriented NiCo2O4 microspheres yielded a high current density (258 mA/g) at 10 mV/s and low overpotential (224 V). The highly active electrode showed efficient electron transportation towards oxygen evolution reaction. Long-term stability over 16 h was achieved by the fabricated high-performance NiCo2O4 electrode. It is recommended that NiCo2O4 microspheres obtained from 3:1 stoichiometry ratio of Ni and Co would lead to new electrocatalysts that give best performance than expensive catalysts used currently in the water oxidation process.

Energy-efficient production of hydrogen through urea electrolysis is still challenging due to the lack of satisfactory catalysts for urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) in urea containing solution. In this study, Ni–WxC/C (x = 1,2) composite with high activity for urea electrocatalysis was prepared by direct electro-reduction of affordable feedstock of NiO–CaWO4–C in molten CaCl2–NaCl at 873–973 K. The addition of graphite in precursor decreases the particle size of Ni. Introducing WxC into Ni particles can reduce the overpotential for UOR. As a result, the obtained Ni-WxC/graphite composite exhibits high current density for urea oxidation, which is about 11-folds and 52-folds higher than that of Ni/graphite and Ni (@1.53 V vs. RHE), respectively. After changing the carbon source from graphite to CNTs, the anodic current density was further increased by 43%, reaching 50.31 mA cm−2. Moreover, the cathodic catalyst WxC/CNTs obtained by the same preparation process exhibits high performance towards HER, with a low onset potential of 131.5 mV and a Tafel slope of 69.5 mV dec−1. Assembling an electrolyzer using Ni-WxC/CNTs as anode and WxC/CNTs as cathode can yield a current density of 10 mA cm−2 at merely 1.65 V in 1 M KOH/0.33 M urea aqueous solution, with excellent long-term electrochemical durability. The environmental-friendly production process uses affordable feedstocks for the synthesis of efficient catalysts toward urea electrolysis, promising an energy-saving hydrogen production as well as waste treatment.

Low-cost yet high-efficiency oxygen evolution reaction (OER) catalysts have attracted ardent attention to speed up the development of water electrolysis. Recent researches have shown that layered double hydroxides (LDH) are promising candidates towards OER, but further improvement is still highly demanded for its large-scale practical application in water splitting. Herein, we report a 3D P-doped MoO3/FeCo LDH/NF (P–MoO3/FeCo LDH/NF) ultrathin nanosheet heterostructure electrocatalyst with an extremely low overpotentials of 225 mV for delivering a current density of 10 mA cm−2 for OER and a great durability for at least 80 h by a simple one-step hydrothermal method. Extraordinarily, the P–MoO3/FeCo LDH catalyst achieves a high current density of 300 mA cm−2 and even 350 mA cm−2 at an extremely low overpotential of 297 mV and 302 mV, respectively, which is crucial for the water electrolysis industry. The remarkable performance may be attributed to that the heterostructure between P–MoO3 and FeCo LDH not only optimizes electronic structure, thus inducing electron transfer from P–MoO3 to FeCo LDH and then realizing fast electron transfer rates, but also produces more catalytic active sites. Moreover, the synergetic effect between MoO3 and FeCo LDH also plays an essential role for enhancing the catalytic performances. This work explores the effect of phosphomolybdic acid on the structure, composition and performances of FeCo LDH catalysts, and also provides a simple and cost-effective way to prepare high-efficiency and low-cost layered double hydroxide electrocatalysts for OER.

A straightforward, one-step route has been established to fabricate reduced- (rGO) and nitrogen-doped reduced graphene oxide (NrGO) with remarkable lithium-ion storage properties. The graphene oxide (GO) was synthesized as starting material by improved Hummers’ method. Thereafter, thermally annealing GO with NH3 at elevated temperature to synthesize NrGO was yielded a more open structure with nitrogen sites suitable for enhanced Li intercalation. NrGO exhibited a reversible capacity of 240 mAhg−1 at 10 Ag-1 after 500 cycles with 90% capacity retention, which is the best result achieved among graphene oxide-based anodes at this current density. In contrast to rGO, NrGO cells exhibited a gradually increasing capacity profile, reaching up to 114% of the initial capacity at 0.1, 2, and 10 Ag-1 current densities. Results showed that high occupancy of pyridinic N within NrGO enhanced battery performance and cell kinetics upon cycling which offers long-time operability at high current density.

In this study, we present the synthesis of pristine carbon (p-CNO), nitrogen doped (N–CNO) and oxygen functionalized (ox-CNO) nano onions, using flame pyrolysis, chemical vapour deposition, and reflux methods, respectively. Pd/p-CNO, Pd/N–CNO and Pd/ox-CNO electrocatalysts are prepared using a simple and quick microwave-assisted synthesis method. The various CNO and Pd/CNO electrocatalysts are fully characterized and the FTIR and XPS results reveal that the synthesized CNOs contain oxygen and nitrogen functional groups that facilitates the attachment and dispersion of the Pd nanoparticles. Electrochemical tests show that the N–CNO and Pd/N–CNO electrocatalysts exhibit high current density (4.2 mA cm −2 and 17.4 mA cm −2), long-term stability (1.2 mA cm −2 and 6.9 mA cm −2), and fast electron transfer when compared to the equivalent pristine and oxidized catalysts (and their Pd counterparts), and a commercial Pd/C electrocatalyst, towards ethanol oxidation reactions in alkaline medium.

Low-temperature solid oxide fuel cells (LT-SOFCs) have recently gained enormous attention worldwide with a new research trend focusing on single layer fuel cells (SLFC), which have better cell performance than traditional SOFCs at low operating temperatures. In this study, a triple (e−/O2−/H+) conducting perovskite BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) is used as the intermediate layer material for SLFC. A high current density of 994 mA/cm2 at 0.6 V and a peak power density of 610 mW/cm2 with an OCV of 1.01 V has been achieved with a cell operating temperature of 550 °C, confirming the application feasibility of BCFZY in SLFCs. Furthermore, a typical proton conductor BaZr0.8Y0.2O3-δ (BZY) is introduced into BCFZY to enhance the cell performance. By adjusting the mass ratio of the BCFZY-BZY layer, an optimal power density is obtained, achieving 703 mW/cm2 with an OCV of 1.03 V at 550 °C with an 8BCFZY:2BZY (wt%) ratio. These findings prove that the proposed BCFZY-BZY holds great promise for developing SLFCs to realize low-temperature operation.

To design an efficient and cost-effective electrocatalyst based on Prussian blue and its analogs are a promising choice to realize energy transformation and storage via water-splitting. Herein, a facile and practical method is developed to in-situ grow Fe–Co Prussian-blue-analog (PBA) nanocages with an open hole in each face center on Ni(OH)2/NF substrate to form the hierarchical cage-on-plate structure. Furthermore, the Fe–Co PBA nanocages attached to Ni(OH)2/NF plates are hydrogenated and nitrogenized into FeCoNi/NF and FeCoNiN/NF electrodes, respectively. As-prepared electrodes successfully retain the 3D hierarchical micro-nano structures of Fe–Co PBA@Ni(OH)2/NF precursor and can be used as a bifunctional water-splitting catalyst for overall water splitting. Compared to FeCoNi/NF, FeCoNiN/NF shows more efficiency and durability in the electrolytic water splitting tests in alkaline media. For the FeCoNiN/NF electrocatalyst, ultralow overpotentials for hydrogen evolution reaction (HER) are only 56 and 290 mV at current densities of 10 and 500 mA cm−2. Meanwhile, overpotentials for oxygen evolution reaction (OER) are 267 and 374 mV at current densities of 50 and 500 mA cm−2. The FeCoNiN/NF electrode can act both the cathode and the anode for overall water splitting, this electrolyzer only requires a cell voltage of 1.492 V to afford a current density of 10 mA cm−2. This electrolyzer can stably deliver a viable high current density of 625 mA cm−2 for 40 h to meet the condition of industrial application.

Direct Ethanol Fuel Cells (DEFCs) have fascinated remarkable attention on account of their high current density and being environmentally friendly. Developing efficient and durable catalysts with a simple and fast method is a great challenge in the practical applications of DEFCs. To this end, the bimetallic Pd–Ag with adjustable Pd:Ag ratios were synthesized via a simple and one-pot strategy on activated carbon as a support in this study. The Pd–Ag/C catalysts with different molar ratios were synthesized by simultaneous reduction of Pd and Ag ions in the presence of the ethanolic sodium hydroxide as a green reducing agent for the first time. Several different methods, including FE-SEM, HR-TEM, XRD, XPS EDX, ICP-OES, and BET were used to confirm the structure and morphology of the catalysts. The performance of catalysts was also examined in ethanol oxidation. Obtained results of electrochemical experiments revealed that the Pd3–Ag1/C catalyst had superior catalytic activity (2911.98 mAmg−1Pd), durability, and long-stability compared to the other catalysts. The excellent catalytic characteristic can be attributed to the synergistic effect between Pd and Ag. We presume that our simple method have the chance to be utilized as a proper method for the synthesis of fuel cell catalysts.

Supercapacitors (SCs) have proven remarkable interest in portable digital devices because of their long life span and high power densities. However, low energy densities of SCs hindered their applications due to the lack of high-performance negative electrode materials. In this work, we demonstrated the successful surface engineering of iron oxide nanoparticles (Fe3O4-NPs) by polyaniline (PANI) coating through a facile low-temperature hydrothermal method. The polyaniline coated iron oxide nanoparticles (Fe3O4/PANI-NPs) were characterized by a series of techniques including XRD, FT-IR, RAMAN, XPS, TGA, BET, SEM, and TEM. Fe3O4-NPs and Fe3O4/PANI-NPs are investigated as negative electrode materials for SCs in basic potassium hydroxide (KOH) electrolyte. The Fe3O4/PANI-NPs sample possesses specific capacitance of 1669.18 F g−1 while Fe3O4-NPs exhibits 1351.13 F g−1 at 1 A g−1 at identical conditions. The Fe3O4/PANI-NPs sample exhibits remarkable electrochemical cycling performance (96.5%) over pristine Fe3O4-NPs (92%) at high current density of 15 A g−1 by exceeding the 25,000 times charge/discharge cycles. The PANI coating not only offers a strong shell to avoid degradation of the material but also contributes to enhancing the capacitance with outstanding stability. Furthermore, we analyzed the charge storage contributions by implementing the power's law and interestingly Fe3O4/PANI-NPs sample exhibits high capacitive type storage (85% capacitive at 10 mVs−1). Based on our experiments, Fe3O4/PANI-NPs shows exceptional high electrochemical results in basic electrolyte with excellent stability and surpass most of recently reported work based on the iron oxides and their composites. Therefore, the proposed strategy can be applied to fabricate the high-performance negative electrode materials for supercapacitors.

It is well-known that flow field design is of primary importance to optimization of proton exchange membrane (PEM) fuel cell. Traditional channel-rib flow fields, e.g. parallel or serpentine channels, always lead to non-uniform distributions of reactant gas, liquid, current density and so on between the channel and rib regions. Metal foam materials with high porosity (>90%) have been proposed as alternative flow fields for PEM fuel cells. In this study, influences of metal foam flow field on the transport phenomena coupled with the electrochemical reactions in PEM fuel cell are investigated using a three-dimensional (3D) multi-phase non-isothermal model. Specifically, the full morphology of metal foam flow field is taken into account in the 3D simulation after validated against experimental permeability data. The full morphology inclusion enables capture of the detailed gas flow from the flow field into the gas diffusion layer (GDL) and the current collection at the metal foam/GDL interface. In addition, compared with the conventional channel-rib flow fields, the metal foam design greatly increases fuel cell performance in the high current density regime. In addition, the oxygen and current density distributions in PEM fuel cell with the metal foam flow field are more uniform than those in the conventional one. Though the current collection area at the GDL surface is much smaller in the metal foam flow field, the relevant Ohmic loss won't increase significantly due to the improved physical contact by the fine pore structure of metal foam over the GDL.

Mn-based Prussian blue analogue is regarded as one of the promising cathodes for sodium ions battery owing to its high theoretical capacity and low cost. However, the unstable structure during charging/discharging process and the poor cycle life hinder its commercial application. In this work, potassium ions stabilized hollow Mn-based Prussian blue analogue is synthesized through a simple sodium citrate assisted method using for cathode of sodium-ions batteries. Although unique hollow structure could suffer volume variation during charging/discharging process, the K+ is introduced to further stabilize its structure. The PBAs cathode exhibits a high reversible specific capacity of 128 mA h g−1 at 50 mA and superior rate performance of 72 mA h g−1 at a high current density of 3200 mA g−1, which is attributed to its stable structure and enhanced sodium ions transport kinetics. Ex-situ XRD/Raman tests and electrochemical measurements further prove the synergistic effect of various alkali ions (K+/Na+) and unique hollow structure. They work together to improve the structural stability and promote sodium ions diffusion rate of Mn-based PBAs.

Proton exchange membrane fuel cells (PEMFCs) have become the most attractive power supply units for stationary and mobile applications. The operation, design characteristics, as well as performance of PEMFCs, are closely related to the multiphase transport of mass, heat, and electricity in the cell, a critical of which is the gas diffusion layer (GDL). It is very important to guarantee the transmission of water and gasses under high current density, and which is the weakness of PEMFCs at present. Microporous layer (MPL) is considered to be the key variable for mass transfer, so varieties of works focus on modification of MPL materials and its structure design. However, there is still a lack of special review to summarize and prospect the progress of MPL in recent years. This review article therefore focuses on the insights and comprehensive understanding of four critical issues of the MPL, the porosity, pore size distribution, wettability, structural design and the durability of MPL. At last, the conclusion and recommendations section summarized the future prospects and recommendations for possible research opportunities.

Ni–Fe-alloy-foam supported solid oxide electrolysis cell with an arrangement of nickle and Sc0.1Ce0.005Gd0.005Zr0.89O2 (Ni-SCGZ) cathode, SCGZ electrolyte and Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) anode is successfully fabricated by the sequence wet-chemical coating. The multi-layer cathode with a gradient of thermal expansion coefficient (TEC) is deposited on the alloy-foam support. Two-step firing processes are applied including cathode pre-firing (1373 K, 2 h) and electrolyte sintering (1623 K, 4 h) using slow heating rate enhanced with compressive loading. The fabricated cell shows current density of −0.95 Acm−2 at 1.1 V with H2O:H2 = 70:30 and 1073 K, providing hydrogen production rate at 4.95 × 10−6 mol s−1. However, performance degradation was observed with the rate of 0.08 V h−1, which can be ascribed to the delamination of BSCF anode under operating at high current density.

Nickel modified titanium dioxide nanotubes (TiO2-NTs/Ni) and TiO2-NTs electrodes are investigated for hydrogen evolution reaction (HER). To obtain large surface area, TiO2-NTs are prepared by using anodization method at a constant voltage of 60 V for various anodization times (30 min, 1 h and 2 h). Small amount of Ni is successfully deposited over TiO2-NTs via electrodeposition method. Hydrogen evolution activities of TiO2-NTs/Ni and TiO2-NTs are investigated in 1 M KOH solution at room temperature. Characterizations of prepared nano structured electrodes are analyzed with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and cyclic voltammetry (CV) and electrochemical-activities are determined through cathodic current-potential curves and electrochemical impedance spectroscopy (EIS). Hydrogen volumes produced from prepared electrodes are also measured under constant voltage of 3 V for 30 min. Obtained results showed that hydrogen evolution activity increased with the modification of TiO2-NTs by nickel. High current density at specific overpotentials, hydrogen volume and small polarization resistance are obtained on TiO2-NTs/Ni. High stability and durability are also obtained on this electrode. So, TiO2-NTs/Ni as an electrocatalyst is suggested to use in water electrolysis systems. (c) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Multi-functionality is a highly desirable feature in designing new electrode material for both energy storage and conversion devices. Here, we report a well-integrated and stable β-NiMoO4 that was fabricated on three dimensional (3D) nickel foam (NF) by a simple hydrothermal approach. The obtained β-NiMoO4 with interesting honeycomb like interconnected nanosheet microstructure leads to excellent electrochemical activity. As an electrode for Supercapatteries, β-NiMoO4–NF showed a high specific capacity of 178.2 mA h g−1 (916.4 F g−1) at 5 mA cm−2 current density. Most importantly, the fabricated symmetric device exhibits a maximum specific energy of 35.8 W h kg−1 with the power output of 981.56 W kg-1 and excellent cyclic stability. In methanol electro-oxidation, the β-NiMoO4 –NF catalyst deliver the high current density of 41.8 mA cm−2 and much lower onset potential of 0.29 V with admirable long term stability. Apart from the above electrochemical activity, the β-NiMoO4 –NF honeycomb microstructure demonstrates a promising non-noble electrocatalyst for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) and showed a considerable overpotential of 351 mV (OER) and 238 mV (HER). The attractive multifunctional electrochemical activity of β-NiMoO4–NF could be originates from their unique honeycomb micro/nano structure which can acts as an “ion reservoir” and thus leads to superior energy storage and conversion processes.

The mainstream of pyrolyzed transitional metal-nitrogen-carbon (M-N-C) catalysts for ORR still confront difficulty in PEMFC application. To pursue M-N-C structure from wet chemistry at ambient temperature, this paper prepares FexCoy-PANI/CNT porous structures composed of amorphous Fe and Co NPs into PANI layer on CNT surface, supported by the controlled molecular self-assembly mechanism (MS). For their ORR behaviors in acid medium, all FexCoy-PANI/CNT catalysts demonstrate similar features as Pt-based catalyst in low current density region, and 4e pathway and active sites in pore utilization in high current density region. Specifically, we disclosed nitrogen in PANI matrix dominates specific activity for ORR, and a little transitional metal attain mass activity at maximum. The active sites mounted into PANI matrix and 4e pathway help catalysts to achieve high durability. Thus, we extend a new type of platinum-free catalyst and develop a bottom-up approach for preparation-structure-activity, expecting to drive PEMFC remarkably.

Metal phthalocyanine-linked conjugated microporous polymers (MPc-CMPs) have huge potential applications in energy conversion and storage systems. However, the inherent low conductivity limits their practical application. Herein, the MPc-CMPs are hybridized with highly conductive carbon nanotubes (CNTs) via the easy vacuum filtration method. Interestingly, the composite (denoted as CoPc-CMP/CNTs) shows the flexible feature, which can be served as the flexible binder-free electrode for supercapacitors (SCs). As expected, the flexible CoPc-CMP/CNTs exhibits a high specific capacitance of 289.1 F g−1 at a current density of 1 A g−1 and good capacity retention of 82.4% over 1350 cycles at a high current density of 10 A g−1. Furthermore, First-principle calculations are used to elucidate the superiority of CoPc-CMP to other analogues. The good electrochemical performance could be attributed to the synergistic effect from the high pseudocapacitance and good conductivity of CoPc-CMP as well as the capacitive contribution and good conductivity of CNTs. Our strategy provides a new avenue to develop the high-performance SCs via rational integration of MPc-CMPs with highly conductive CNTs.