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Two geometrical parameters, amplitude and wavelength, of the structure of the wavy-flow field in a proton exchange membrane fuel cell (PEMFC) were investigated on their impacts on cell performances via a three-dimensional, multiphase, and non-isothermal model. Amplitude and wavelength significantly influence oxygen transport, friction resistance, and current densities in PEMFC operations. The enhancement of current density peaks at an amplitude of 0.4 mm and a wavelength of 2 mm, increased by 10.40% compared to the non-wavy design. The wavy channels would increase the oxygen concentration gradient and the viscous friction, increasing entropy generation. The entropy generation rates increase more significantly at small wavelengths and large amplitudes. The entropy generation ratio (EGR) evaluates the performances of different wavy channels based on the accurate description of oxygen transport in PEMFC without calculating the associated pumping power consumption rates. The EGR decreases with decreasing wavelength or increasing amplitude. • Entropy generation by mass transport and friction is greatly influenced by flow field types. • The entropy generation analysis is introduced to verify the superiority of flow fields. • EGR is proposed for the evaluation of oxygen transport under unequal pumping power consumptions. [ABSTRACT FROM AUTHOR]

In this study, a kW-grade air-cooled proton exchange membrane fuel cell (PEMFC) stack with a dead-end anode (DEA) operation is designed and manufactured. The gravity-assisted drainage principle is applied for the stack to design the wettability of gas diffusion layers (GDLs) and the anode channel geometry, which can help the liquid water that diffuses to the anode to drain out of the anode porous electrode and move down the anode channel outlets. As a result, the stack can stably operate in a long purge interval of 268 s and in a short purge time of 2 s. In addition, using this design, only four small-power fans are employed to pump air to the cathode to provide oxygen for the electrochemical reaction and cool the stack. With a constant load current of 30, 45, or 60 A, the stack output voltage is experimentally tested at various cathode air flow rates (CAFRs). The local temperatures (60 measurement points) inside the stack and the pressure differences across anode channels are also monitored to understand heat dissipation and the back diffusion of liquid water. In a wide range of operating conditions, the designed stack possesses superior and stable voltage output characteristics with relatively uniform temperature distributions. The measured maximum output power is 3.83 kW, and the parasitic powers of fans are only 80∼112 W. • A kW-grade air-cooled PEMFC system under dead-ended anode operation is designed. • The effect of cathode air flow rate on dynamic temperature evolution is studied. • Modified anode channels based on gravity drainage are applied to the cell system. • A stringing fan arrangement is used to improve cooling efficiency. [ABSTRACT FROM AUTHOR]

The effect on the slag formation behavior in the softening melting zone of a hydrogen-rich blast furnace is investigated by charging iron coke to the iron ore and controlling different volume fractions of hydrogen. The reduction mechanism of iron coke to iron ore under hydrogen-rich conditions is expounded that iron coke and hydrogen increase the concentration of CO around iron ore and promote its further reduction. The participation of iron coke and hydrogen promotes that FeO is reduced to Fe in iron ore, which prompts the production of high melting point substances in slag. The melting point of slag iron increases the melting start temperature. Hydrogen and iron coke promote the carburization of dripping iron so that molten iron drips quickly, which narrows the melting drop interval. From the perspective of the maximum pressure difference and the comprehensive permeability S value, the blast furnace permeability will be improved. • The effect on soft molten drop zone of hydrogen and iron coke. • The reduction mechanism is expounded with hydrogen and iron coke. • The slag melting point rises and molten iron carburization is promoted. • The permeability of the softening melting zone is improved with hydrogen and iron coke. [ABSTRACT FROM AUTHOR]

The membrane electrode assembly (MEA) of a proton exchange membrane fuel cell (PEMFC) would deform when there is a pressure difference between the cathode and anode. In this study, a three-dimensional PEMFC model that incorporates a two-dimensional MEA deformation model is employed to investigate the effects of the curved MEA on oxygen transport, liquid water removal, pressure drops across cells, and resulting overall cell performances. The results show that the MEA deformation generates a gap between the rib and gas diffusion layer (GDL), thereby enhancing the oxygen transport into and liquid water removal from the cathode porous electrode. At an operating voltage of 0.4 V, the output current density is enhanced by 4.83%, 6.67%, and 8.61%, respectively, for the pressure differences of 10, 20, and 30 kPa between the cathode and anode, as compared with that without a pressure difference. An efficiency evaluation criterion (EEC) that represents a tradeoff between mass transfer enhancement and pressure drop penalty is introduced to evaluate the overall cell performance enhancement. The result shows that the EEC value increases with increasing the pressure difference between the cathode and anode, confirming the performance enhancement by the deformed MEA. In addition, the effects of MEA deformation are also examined at two sets of channel heights (H) and widths (W), i.e., W H =0.5 mm and W H =1.5 mm. At an operating voltage of 0.4 V, the output current density is enhanced by 20.18% at a pressure difference of 30 kPa for the cell with W H =0.5 mm, whereas it is improved only by 2.91% for the cell with W H =1.5 mm. Therefore, increasing the pressure difference between the cathode and anode is a more effective approach to performance enhancement for the cell with a small channel height and width. • The MEA deformation caused by cathode and anode pressure differences is studied. • A gap is generated between the bipolar plate and deformed MEA. • Oxygen transport and liquid water removal are enhanced by the gap. • Cell performances are improved by the deformed MEA. [ABSTRACT FROM AUTHOR]

The effect of replacing coke with iron coke on iron-ore softening, melting, and dripping in a blast-furnace hydrogen (H 2)-rich atmosphere is studied. When H 2 content increases from 0% to 100%, the iron-ore softening start temperature decreases and then increases. The softening end temperature rises continuously. H 2 promotes ferrous oxide (FeO) reduction; thus, more high-melting-point substances are generated in the slag, the melting start and dripping temperatures trend upward, the melting–dripping range narrows, and the charge permeability improves. Replacing iron coke with ordinary coke, for 0–20% H 2 , the iron-ore softening start and end temperatures further decrease and increase, respectively. The dripping range rises and narrows, slightly improving the permeability. For H 2 >20%, the iron coke has no impact on the iron-ore softening–melting behavior. Compared with coke, the iron coke after reaction has severe dissolution loss and obvious strength reduction, coke should not be completely replaced by iron coke. • Hydrogen is injected into a blast furnace at different proportions. • In addition, traditional coke is replaced with iron coke in the blast furnace. • More high-melting-point substances are found in the slag. • The melting–dripping zone narrows and the burden permeability improves. • The iron-coke strength decreases in the hydrogen-rich atmosphere. [ABSTRACT FROM AUTHOR]

The design of multi-components nanostructure with interface heterojunction is the cutting-edge research in recent years because the catalytic activity, stability, and durability of catalysts are highly affected by the strong electronic effects, geometric effects, and synergistic effects occurring at the interface. Based on this, an efficient bifunctional electrocatalyst embedding highly dispersed Ni 2 P/Co nano heterojunction at the porous hollow-out carbon shell is developed for overall water splitting through evenly epitaxial growth of ultrathin Ni 2 P nanosheets on Co-based ZIF-67. The distinct electron interaction between the interfacial Ni 2 P (300) and Co (100) effectively lowers the overpotential of OER (316 mV vs. RHE) and HER (149 mV vs. RHE) at the current density of 10 mA cm−2. Density functional theory (DFT) calculation further identifies that the Ni 2 P and Co heterojunctions optimize the adsorption energy of intermediate products and lower the energy barrier of the rate-determining step of OER significantly. This work provides a rational design of a well-defined interface toward overall water splitting electrocatalysts and offers a scientific basis for an in-depth understanding of the mechanism of the catalysts with nano heterojunction. • Synthesis a highly dispersed Ni 2 P/Co nano heterojunction catalyst at the porous hollow-out carbon shell. • The nano heterojunction is composed of Ni 2 P (300) and Co (100) crystal face. • Low overpotential of 316 mV and 149 mV are required at 10 mA/cm2 for OER and HER in 1 M KOH respectively. • Present a low cell voltage of 1.56 V at 10 mA/cm2 for overall water splitting. [ABSTRACT FROM AUTHOR]

Working temperature is a critical parameter that influences the performance of proton exchange membrane fuel cells (PEMFCs). Appropriate thermal management can improve the efficiency of PEMFCs and prevent irreversible internal damage such as membrane degradation. To solve the slow response and poor dynamic performance of traditional temperature control strategies, the dynamic temperature mode of PEMFCs is established and a temperature control strategy based on the sparrow search algorithm-proportional integral differential (SSA-PID) is proposed in this study. The performance of the SSA-PID temperature control is verified by the simulations of current step change, vehicle dynamic load, and working parameter variation. The results show that the proposed method has the advantages of fast convergence, better dynamic performance, and anti-disturbance ability. The maximum power density of the SSA-PID temperature controller is 6.58% and 12.94% higher than GA (genetic algorithm)-PID and traditional PID controllers, respectively. Moreover, the proposed method can ensure temperature fluctuations within 0.5 K under dynamic disturbance. • The PEMFC temperature control strategy based on sparrow search algorithm is proposed. • The performance of the temperature control strategy under external disturbance is discussed. • The proposed control method is compared with the GA-PID and traditional PID controllers. • The proposed method can ensure temperature fluctuations within 0.5 K. [ABSTRACT FROM AUTHOR]

Integrating transition metal complexes with carbon-based materials, especially graphene, is a useful strategy for synthesizing effective hydrogen evolution catalysts. Herein, we report a design of hollow hexagonal NiSe–Ni 3 Se 2 nanosheets grown on reduced graphene oxide (NiSe–Ni 3 Se 2 /rGO) by a simple hydrothermal method as an effective catalyst for hydrogen evolution reaction (HER) in the full pH range. In 0.5 M H 2 SO 4 , the NiSe–Ni 3 Se 2 /rGO possesses 112 mV to achieve 10 mA cm−2 and a small Tafel slope (61 mV dec−1). In 1.0 M PBS and 1.0 M KOH, the overpotentials are 261 and 188 mV at 10 mA cm−2, and Tafel slopes are 103 and 92 mV dec−1, respectively. Meanwhile, it owns good cycle stability and durability over 20 h in the whole pH range (0-14). In all solutions, the HER performance of NiSe–Ni 3 Se 2 /rGO is better than that of NiSe–Ni 3 Se 2. This is because the rGO substrate accelerates the electron transfer and improves the electrical conductivity, increasing HER activity of catalyst. • The hollow hexagonal NiSe-Ni3Se2 nanosheets uniformly decorate the rGO. • The hollow structure exposes more active sites and transport pathways. • The hybrid material exhibits superior performance for HER in all pH media. • The stability of the composite is good under a variety of pH conditions. [ABSTRACT FROM AUTHOR]

The highly porous electrode of a crisscrossed CoNi nanosheets array grown on reduced graphene oxide decorated Ni foam (CoNi/rGO@Ni foam) is fabricated through a facile dip and dry method followed by electroreduction and electrodeposition methods. The phase composition and morphology of the electrode are characterized by XRD, SEM, TEM, and EDS. In single electrode tests, CoNi/rGO@Ni foam electrode displays an excellent catalytic performance (330 mA cm−2 at 0.6 V) and stability towards urea electrooxidation when comparing to Ni foam and CoNi nanosheets modified Ni foam (CoNi@Ni foam) electrode. Besides, a low initial oxidation potential of urea electro-oxidation to 0.14 V is achieved on the CoNi/rGO@Ni foam electrode. The introducing of rGO to the electrode greatly reduced the reaction activation energy from 14.47 to 10.35 kJ mol−1. Besides, large active surface area (261.67 cm2) is also obtained from the electrode. The CoNi/rGO@Ni foam anode exhibits a maximum power density of 12.58 mW cm−2 in direct urea-hydrogen peroxide fuel cell tests. Excellent performance shows in single electrode tests and fuel cell tests suggest that addition of rGO to the electrode is an easy and feasible method to enhance the performance of the catalyst. • Highly porous electrode: crisscrossed nanosheets array grows on rGO modified Ni foam. • The influence of rGO on the catalytic performance of the electrode was researched. • Low initial oxidation potential towards urea electro-oxidation was obtained. • Achieved an excellent performance and stability when practical use in DUHPFC. [ABSTRACT FROM AUTHOR]

Seeking the efficient and robust electrocatalysts necessarily enhances performance of hydrogen evolution reaction (HER). Increasing the surface active sites is a means to improve the performance. Herein, we use the Ni 0·85 Se anchored on reduction of graphene oxide (Ni 0·85 Se/rGO) hybrid material skillfully established by one-step facile hydrothermal method as a robust and stable electrocatalyst applying to hydrogen evolution reaction (HER). In terms of morphology, Ni 0·85 Se nanospheres composed of many nanosheets are uniformly distributed on the graphene sheet layer. We also detailedly analyze its properties. Based on the interaction between Ni 0·85 Se and rGO, and the roles of graphene are as a substrate to heighten conductivity, possesses more active surface area by limiting growth of Ni 0·85 Se, and increases dispersion for exposing more active surface area and enlarge ion/electron transfer rate. In HER, the Ni 0·85 Se/rGO catalyst displays the overpotential of 128 mV with a common current density of 10 mA cm−2, a small Tafel slope of 91 mV dec−1, an extremely low onset potential of 37 mV, outstanding stability that a high current retention of 97.7% after 1000 cycles and well long-term stability for 18 h, outperforming the capability of Ni 0·85 Se nanospheres in alkaline solution for HER. The above results indicate that the Ni 0·85 Se/rGO hybrid material is a good HER ability and non-noble metal electrocatalyst has potential value in HER. • The Ni 0.85 Se nanospheres uniformly decorate the rGO sheets. • The Ni 0.85 Se/rGO electrocatalyst possesses more active surface area. • The stability of the composites can reach 97.7%. • The hybrid material exhibits superior performance for HER. [ABSTRACT FROM AUTHOR]

Herein, the vertical thin nickel–iron layered double hydroxide nanosheets grown on the hills-like nickel framework (NiFe LDH/Ni@NF) are employed for the oxygen evolution reaction (OER), securing at the low overpotentials of 197 and 270 mV to obtain the current densities of 20 and 100 mA cm−2, respectively, with a Tafel slope of 73.34 mV dec−1. The electrodeposited nickel film induces the NiFe LDH nanosheets grow vertically and thinly. As well, the nickel abundant interfaces and inner space makes this catalyst effective for OER. It was further served as the OER electrode in a water splitting system coupled the Pt/C cathode, and a cell voltage was at 1.52 and 1.67 V to achieve the current density of 10 mA cm−2 and 50 mA cm−2. In addition, the water electrolyzer can suffer a long time of 24 h at 50 mA cm−2, showing the feasibility in a practical unbiased alkaline water splitting system. • The vertical thin Ni 4 Fe 1 LDH-16h was prepared on the hills-like nickel framework. • The crosslinked nanosheets can offer amounts of active sites for OER. • It achieves a low overpotential of 197 mV to drive 20 mA cm−2 for OER. • The assembled electrolyzer exhibits enhanced performance. [ABSTRACT FROM AUTHOR]

In this paper, we report the three-dimensional self-supported CoMoO 4 nanosheet clusters on the nickel foam (denoted as CoMoO 4 /NF) by a facile hydrothermal-calcination method for efficient hydrogen generation. As a result, the freestanding CoMoO 4 electrode exhibits an efficient electrochemical activity towards hydrogen evolution reaction, showing overpotentials as low as 68 and 178 mV at current densities of 10 and 100 mA cm−2 in the alkaline condition (1 M KOH), respectively, a Tafel slope value of 82 mV per decade. Moreover, the electrode exhibits remarkable electrochemical durability for 1000 cycles. Significantly, the water splitting electrolyzer assembled with CoMoO 4 /NF || NiFe LDH/NF (the nickel iron layered double hydroxide supported on the nickel foam) system achieved 20 mA cm−2 at 1.63 V, showing the CoMoO 4 /NF is promising for practical water splitting applications. • The low-cost and effective transition metal oxide of CoMoO 4 was adopted for hydrogen generation. • The open nanostructure can facilitate permeating electrolyte as well as releasing hydrogen molecules. • The crosslinked nanosheet clusters can offer amounts of active sites for hydrogen evolution reaction. [ABSTRACT FROM AUTHOR]

Abstract At present, there is an urgent need for plentiful non-noble metal catalyst to substitute for valuableness platinum based metal catalyst in electrochemical water splitting. Here, we fabricated a three-demensional (3D) Ni Co NiCo 2 O 4 nanosheets electrocatalyst that directly grew on Ni foam firstly and then were reduced in 0.1 mol dm−3 sodium borohydride solution. This electrode exhibited high activity in 1.0 mol dm−3 KOH solution with an onset potential of ∼40 mV and a tafel slope of 77 mV dec−1. Furthermore, the Ni Co NiCo 2 O 4 /NF electrode showed a splendid durability during long-playing electrochemical test. Our work may provide an inexpensive, easy-to-obtain and excellent catalyst candidate for future electrolytic water research and industry studies that may involve hydrogen applications in the future. Highlights • The Ni Co NiCo 2 O 4 /NF is an inexpensive, easy-to-obtain and excellent electrode. • When the current density up to 10 mA cm−2 requires an overpotential 125 mV. • Metallic Ni and Co core enhance the electrode activity. [ABSTRACT FROM AUTHOR]

Porous Ni 2 P nanoflower supported on nickel foam (Ni 2 P@Ni foam) electrodes are synthesized via a simple hydrothermal growth strategy accompanied with further phosphating treatment. The prepared electrodes are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). Electro-catalytic performances towards urea electro-oxidation are tested by cyclic voltammetry (CV), chronoamperometry (CA) coupled with electrochemical impedance spectroscopy (EIS). By phosphating Ni(OH) 2 precursor, the final obtained Ni 2 P@Ni foam electrode presents a porous Ni 2 P nanoflower structure within abundant porosity, and so exposes a large amount of electro-catalytic active sites and electronic transmission channels to accelerate the interfacial reaction. Compared with Ni(OH) 2 @Ni foam precursor, the Ni 2 P@Ni foam catalyst exhibits more excellent electro-catalytic activity as well as lower onset oxidation potential. Remarkably, the Ni 2 P@Ni foam catalyst reaches a peak current density of 750 mA cm −2 with an onset oxidation potential of 0.24 V (vs. Ag/AgCl) accompanied by an excellent stability in 0.60 M urea with 5.00 M KOH solutions. Benefiting from the unique porous nanosheet structure, the as-synthesized Ni 2 P@Ni foam catalyst performs a highly enhanced catalytic behavior for alkaline urea electro-oxidation, indicating that the material can be hopefully applied in direct urea fuel cells. [ABSTRACT FROM AUTHOR]

A binder-free and flexible Au electrode is prepared by spontaneous deposition of Au onto a A4 (A4-paper)-8B (8B pencil)-Ni Film substrate (ABNi) which is assembled by electrodeposition of nanoscale Ni particles on the surface of A4 paper coated by 8B pencil. The morphology and phase structure of the (A4-paper)-8B (8B pencil)-Ni Film-Au (ABNiAu) electrode are characterized by scanning electron microscopy equipped with energy dispersive X-ray spectrometer and X-ray diffractometer. The catalytic activity of the ABNiAu electrode for NaBH 4 electrooxidation is investigated by means of cyclic voltammetry and chronoamperometry. The electrode exhibits a high electric conductivity and the activity substance attaches to the surface of paper substrate tightly and does not fall off at all and the nanoscale Ni and Ni Au alloy enhance the broken of the B H bond in the BH 4 − , all of which lead to a high catalytic activity for NaBH 4 electrooxidation. The oxidation current density reaches 300 mA cm −2 in 1 mol dm −3 NaOH and 0.1 mol dm −3 NaBH 4 at −0.2 V. The exchanged electrons (n) is 6.0 (8.0 in theory), which indicates that the ABNiAu electrode has much higher utilization efficiency of the fuel than our reported LaNi 5 /Pd (n = 4) electrode. [ABSTRACT FROM AUTHOR]

Thorn-like Ni@TiC NAs and flake-like Co@TiC NAs electrodes without any conductive agent and binder are simply fabricated by the potentiostatic electrodeposition of Ni and Co catalysts on the TiC nanowire arrays (NAs). The electrocatalytic activity of H 2 O 2 oxidation on the Ni@TiC NAs electrodes is better than that on the Co@TiC NAs electrodes. The Ni@TiC NAs electrodes demonstrate a rough surface and have many nano-needles on the rod edges, which assures the high utilized efficiency of Ni catalysts. These particular three-dimensional structures may be very suitable for H 2 O 2 electrooxidation. The anodic current of Ni@TiC NAs anode reaches 0.32 A cm −2 at 0.3 V in 1.0 M H 2 O 2 + 4 M KOH solution. The DPFCs employing Ni@TiC NAs anodes display the peak power density of 30.2 mW cm −2 and open circuit voltage of 0.90 V at 85.1 mA cm −2 with desirable cell stability at 10 mL min −1 flow rate and 20 °C, which is much higher than those previously reported. [ABSTRACT FROM AUTHOR]