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The concentrated solar flux distributions of a sixteen-dish concentrator (SDC) were measured applying a thermal infrared imager in combination with water-cooled Lambert target, and predicted using a Monte Carlo ray tracing method (MCRT). A slope error of 2.2 mrad is detected by comparing the experimental and numerical results. Then, a two-stage concentrator system, formed by the SDC in tandem with a three-dimensional compound parabolic concentrator (3D CPC–SDC), is constructed based on the geometrical optics approach. The interception performances and the energy concentration ratio images (ECR) are presented for both the SDC and the 3D CPC–SDC. The results show that the ECR profiles of the SDC depend on the receiver sizes, whereas that of the 3D CPC–SDC is rather steady because most sunlight enters the receiver via several reflections with the 3D CPC mirror. The 3D CPC–SDC is capable of increasing the geometric concentration ratio (GCR) at the expense of a little interception efficiency.

An energy transfer and conversion model for high-temperature solar cavity receivers has been developed using the transport behaviour of solar radiation as described by the spectral radiative exchange factors. A Monte-Carlo ray-tracing method coupled with optical properties was adopted, to predict radiation characteristics of the solar collector system by calculating radiative exchange factors. A cavity receiver with a plano-convexo quartz window was proposed, based upon the directional characteristics of the focal flux and the redistribution effect of the quartz window. Parametric studies on the windowed receiver provided a more uniform flux distribution, higher efficiency and lower loss than the windowless receivers. The predicted results serve as a design reference for the solar receivers or reactors in high-temperature applications.

The nanocrystalline and amorphous Mg 2 Ni-type alloys with nominal compositions of Mg 2 Ni 1−x Mn x ( x = 0, 0.1, 0.2, 0.3, 0.4) were synthesized by melt spinning technique. The structures of the as-cast and spun alloys were characterized by XRD, SEM and HRTEM. The hydrogen absorption and desorption kinetics of the alloys were measured by an automatically controlled Sieverts apparatus. The electrochemical hydrogen storage performances were tested by an automatic galvanostatic system. The results show that the as-spun ( x = 0) alloy holds a typical nanocrystalline structure, whereas the as-spun ( x = 0.4) alloy displays a nanocrystalline and amorphous structure, confirming that the substitution of Mn for Ni facilitates the glass formation in the Mg 2 Ni-type alloy. The hydrogen absorption capacity of the alloys first increases then decreases with rising Mn content, but the hydrogen desorption capacity of the alloys grows with increasing Mn content. Furthermore, the substitution of Mn for Ni significantly improves the electrochemical hydrogen storage performances of the alloys, involving both the discharge capacity and the electrochemical cycle stability. With an increase in the amount of Mn from 0 to 0.4, the discharge capacity of as-spun (30 m/s) alloy grows from 116.7 to 311.5 mAh/g, and its capacity retaining rate at 20th charging and discharging cycle rises from 36.7 to 78.7%.

In order to enhance the glass forming ability of the Mn2Ni-type electrode alloy, Ni in the Mg2Ni compound is partially substituted by Mn. The nanocrystalline and amorphous Mg2Ni-type alloys with nominal compositions of Mg2Ni1−xMnx (x = 0, 0.1, 0.2, 0.3, 0.4) are fabricated by melt-spinning technique. The spun alloy ribbons with a continuous length, a thickness of about 30 μm and a width of about 25 mm are successfully obtained. The microstructures of the as-spun alloy ribbons are characterized by XRD, SEM and TEM. The electrochemical hydrogen storage characteristics of the as-spun alloy ribbons were tested by an automatic galvanostatic system. The electrochemical impedance spectra (EIS) are plotted by an electrochemical workstation (PARSTAT 2273). The hydrogen diffusion coefficients in the alloys are calculated by virtue of potential-step method. The results show that no amorphous structure is detected in the as-spun Mn-free alloy, whereas the as-spun alloys containing Mn display a nanocrystalline and amorphous structure. The amorphization degree of the alloy increases with rising spinning rate, suggesting that the substitution of Mn for Ni facilitates the glass formation in the Mg2Ni-type alloy. The substitution of Mn for Ni markedly improves the electrochemical hydrogen storage performances of the Mg2Ni-type alloy, enhancing both the discharge capacity and the electrochemical cycle stability. Furthermore, the high rate dischargeability (HRD), electrochemical impedance spectrum and potential-step measurements all indicate that the electrochemical kinetics of the alloy electrodes first increases then decreases with increasing amount of Mn substitution.

The nanocrystalline Mg2Ni-type electrode alloys with nominal compositions of Mg20Ni10−xCux (x = 0, 1, 2, 3, 4) were synthesized by the melt spinning technique. The microstructures of the as-cast and spun alloys were characterized by XRD, SEM and HRTEM. The electrochemical hydrogen storage performances were tested by an automatic galvanostatic system. The results show that all the as-spun alloys hold typical nanocrystalline structure instead of an amorphous phase. The melt spinning does not modify the major phase Mg2Ni, but it leads to the formation of crystal defects such as stacking faults, dislocations, sub-grain boundary and twin-grain boundary. The melt spinning significantly improves the electrochemical hydrogen storage capacity of the alloys, whereas it slightly impairs the electrochemical cycle stability of the alloys. The substitution of Cu for Ni significantly ameliorates the electrochemical hydrogen storage performances of the alloys, involving both the electrochemical hydrogen storage capacity and the electrochemical charging and discharging stability.

In order to improve the hydriding and dehydriding kinetics of the Mg2Ni-type alloys, Ni in the alloy was partially substituted by element Cu, and the nanocrystalline Mg2Ni-type Mg20Ni10−xCux (x = 0, 1, 2, 3, 4) alloys were synthesized by melt-spinning technique. The structures of the as-cast and spun alloys were studied by XRD, SEM and HRTEM. The hydrogen absorption and desorption kinetics of the alloys were measured using an automatically controlled Sieverts apparatus. The results show that the substitution of Cu for Ni does not change the major phase Mg2Ni. The hydrogen absorption capacity of the alloys first increases and then decreases with rising Cu content, but the hydrogen desorption capacity of the alloys grows with increasing Cu content. The melt spinning significantly improves the hydrogenation and dehydrogenation capacity and kinetics of the alloys.

In order to improve the electrochemical performance of the La–Mg–Ni system A2B7-type electrode alloys, La in the alloy was partially substituted by Pr and melt spinning technology was used for preparing La0.75−xPrxMg0.25Ni3.2Co0.2Al0.1 (x = 0, 0.1, 0.2, 0.3, 0.4) electrode alloys. The microstructures and electrochemical performance of the as-cast and spun alloys were investigated in detail. The results obtained by XRD, SEM and TEM show that the as-cast and spun alloys have a multiphase structure which consists of two main phases (La, Mg)Ni3 and LaNi5 as well as a residual phase LaNi2. The substitution of Pr for La leads to an obvious increase of the (La, Mg)Ni3 phase and a decrease of the LaNi5 phase in the alloys. The results of the electrochemical measurement indicate that the discharge capacity of the alloys first increases and then decreases with variation of the Pr content. The cycle stability of the alloy monotonically rises with increasing Pr content. When the Pr content rises from 0 to 0.4, the discharge capacity increases from 389.4 (x = 0) to 392.4 (x = 0.1) and then drops to 383.7 mAh/g (x = 0.4) for the as-cast alloy. Discharge capacity increases from 393.5 (x = 0) to 397.9 (x = 0.1), and then declines to 382.5 mAh/g for the as-spun (5 m/s) alloys. The capacity remaining after 100 cycles increases from 65.32 to 79.36% for the as-cast alloy, and from 73.97 to 93.08% for the as-spun (20 m/s) alloy.

In order to improve the hydriding and dehydriding performances of the Mg2Ni-type alloys, Ni in the alloy was partially substituted by element Co, and melt-spinning technology was used for the preparation of the Mg20Ni10−xCox (x = 0–4) hydrogen storage alloys. The structures of the as-cast and spun alloys were studied by XRD, SEM and HRTEM. Thermal stability of the as-spun alloys was researched by DSC. The hydrogen absorption and desorption kinetics of the alloys were measured using an automatically controlled Sieverts apparatus. The results showed that no amorphous phase formed in the as-spun Co-free alloy, but the as-spun alloys containing Co showed certain amount of amorphous phase. The hydrogen absorption capacities of the as-cast alloys first increase and then decrease with the variety of Co content. The hydrogen desorption capacities of as-cast and spun alloys rise with increasing Co content. The rapid quenching significantly improved the hydrogenation and dehydrogenation capacities and the kinetics of the alloys. When the quenching rate increased from 0 (as-cast was defined as spinning rate of 0 m/s) to 30 m/s, the hydrogen absorption capacity of the alloys (x = 0) at 200 °C and 1.5 MPa in 20 min rose from 1.39 to 3.12 wt%, and from 1.91 to 2.96 wt% for the alloy (x = 4). The hydrogen desorption capacity of the alloy (x = 0) in 20 min increased from 0.19 to 0.89 wt%, and from 1.39 to 2.15 wt% for the alloy (x = 4).

In order to enhance the glass forming ability of the Mg2Ni-type hydrogen storage alloy, the Mg in the alloy was partially substituted by La. The alloys Mg20−xLaxNi10 (x = 0, 2, 4, 6) were prepared by casting and rapid quenching. The structures and morphologies of the as-cast and the quenched alloys were studied by XRD, SEM and HRTEM. It was found that no amorphous phase was formed in the as-quenched La-free alloy. But the as-quenched alloys containing La held a major amorphous phase, confirming that the substitution of La for Mg significantly enhances the glass forming ability of the alloys. When La content x ≤ 2, the major phase in the as-cast alloys is Mg2Ni phase, but with the further increase of La content, the major phase of the as-cast alloys changes into (La,Mg)Ni3 + LaMg3 phase. Thermal stability of the as-quenched alloys was studied by DSC, showing that La content engenders a negligible influence on the crystallization temperature of the amorphous phase. The hydrogen absorption and desorption kinetics of the as-cast and the quenched alloys were measured by an automatically controlled Sieverts apparatus. The results showed that the hydrogen absorption and desorption capacities and kinetics of the as-cast alloys clearly rise with increasing La content. For La content x = 2, the as-quenched alloy displays an optimal hydrogen desorption kinetics at 200 °C. The electrochemical measurement showed that the discharge capacities of the as-cast alloys rose with the increase of La content, but those of the as-quenched alloys obtained the maximum values with the variation of La content. The cycle stability of the as-cast and the quenched alloys significantly improved with increasing La content.

In order to investigate the influences of the stoichiometric ratios of B/A (A: gross A-site elements, B: gross B-site elements) and the substitution of Co for Ni on the structure and the electrochemical performances of the AB 2.5 – 3.5 -type electrode alloys, the La–Mg–Ni–Co system La 0.75 Mg 0.25 Ni 2.5 M x ( M = Ni , Co; x = 0 , 0.2, 0.4, 0.6, 0.8, 1.0) alloys were prepared by induction melting in a helium atmosphere. The structures and electrochemical performances of the alloys were systemically measured. The obtained results show that the structures and electrochemical performances of the alloys are closely relevant to the M content. All the alloys exhibit a multiphase structure, including LaNi 2 , ( La , Mg ) Ni 3 and LaNi 5 phases, and the major phase in the alloys changes from LaNi 2 to ( La , Mg ) Ni 3 + LaNi 5 with the variety of M content. The electrochemical performances of the alloys, involving the discharge capacity, the high rate discharge (HRD) ability, the activation capability and the discharge potential characteristics, significantly improve with increasing M content. When M content x increases from 0 to 1.0, the discharge capacity rises from 177.7 to 343.62 mAh/g for the alloy ( M = Ni ) , and from 177.7 to 388.7 mAh/g for the alloy ( M = Co ) . The cycle stability of the alloy first mounts up then declines with growing M content. The substitution of Co for Ni significantly ameliorates the electrochemical performances. For a fixed M content ( x = 1.0 ) , the substitution of Co for Ni enhances the discharge capacity from 343.62 to 388.7 mAh/g, and the capacity retention ratio ( S 100 ) after 100 charging–discharging cycles from 51.45% to 61.1%.

The effects of the substitution of Mn for Ni on the structures and electrochemical characteristics of the as-cast and quenched La 0.5 Ce 0.2 Mg 0.3 Co 0.4 Ni 2.6 - x Mn x ( x = 0 , 0.1, 0.2, 0.3, 0.4) alloys were studied systematically. The results obtained by XRD, SEM and TEM indicate that the as-cast and quenched alloys mainly consist of two major phases the ( La , Mg ) Ni 3 and LaNi 5 and a residual phase LaNi. With increasing Mn content in the alloys, the abundance of the ( La , Mg ) Ni 3 phase decreases and that of the LaNi 5 phase increases and both the lattice parameters and the cell volumes of major phases ( La , Mg ) Ni 3 and LaNi 5 increase. The as-quenched alloys display a nanocrystalline structure, and the grain sizes of the alloys are in a range of 20–30 nm. The results by the electrochemical measurements indicate that the discharge capacities of the as-cast and quenched alloys first increase and then decrease with the variety of Mn content and obtain the maximum values for a Mn content of x = 0.2 . The substitution of Mn for Ni clearly improves the high rate discharge abilities (HRDs) and the activation capabilities of the as-cast and quenched alloys, but it slightly impairs the cycle stabilities of the as-cast and quenched alloys.

The La–Mg–Ni system PuNi 3 -type hydrogen storage alloys La 0.7 Mg 0.3 Co 0.45 Ni 2.55 - x Fe x ( x = 0 , 0.1, 0.2, 0.3, 0.4) were prepared by casting and rapid quenching. Ni in the alloy was partially substituted by Fe in order to improve the cycle stability of the alloys. The effects of the substitution of Fe for Ni combining rapid quenching on the microstructures and electrochemical performances of the as-cast and -quenched alloys were investigated in detail. The results indicate that the substitution of Fe for Ni obviously decreases the discharge capacity and high rate discharge (HRD) capability as well as the discharge potential of the as-cast and -quenched alloys, but it significantly improves their cycle stabilities. The microstructure of the alloys analyzed by XRD, SEM and TEM shows that the as-cast and -quenched alloys have a multiphase structure which is composed of two major phases (La, Mg) Ni 3 and LaNi 5 as well as a residual phase LaNi 2 . The substitution of Fe for Ni leads to an obvious increase in the LaNi 2 phase in the as-cast alloys, and it also helps the formation of a like amorphous structure in the as-quenched alloy. With the increase of Fe content, the grain sizes of the as-quenched alloys significantly reduce, and the lattice constants and cell volumes of the alloys obviously enlarge.

In order to improve the cycle stability of La–Mg–Ni system ( A 2 B 7 -type) alloy electrode, a small amount of Co was added in the La 0.75 Mg 0.25 Ni 3.5 alloy. The effects of Co content on the microstructures and electrochemical performances of the alloys were investigated in detail. The results by XRD and SEM show that the alloys have a multiphase structure which is composed of the LaNi 5 , ( La , Mg ) 2 Ni 7 two major phases and a small amount of the LaNi 2 phase. The cell volumes of the LaNi 5 and ( La , Mg ) 2 Ni 7 phases enlarge with the increasing Co content in the alloys. With the increasing Co content, some electrochemical properties and kinetic parameters of the alloy, involving the discharge capacity, high-rate discharge ability (HRD), the polarization resistance ( R p ) , the loss angle ( ψ ) and the limiting current density ( I L ) , first increase and then decrease. The addition of Co slightly improves the cycle stabilities of the alloy electrodes. The mechanism of the efficiency loss of the experimental alloy was investigated by means of SEM and X-ray photoelectron spectroscopy (XPS). The results indicate that the fundamental reasons for the capacity decay of the La 0.75 Mg 0.25 Ni 3.5 Co x ( x = 0 , 0.2 , 0.4 , 0.6 ) alloy electrodes are the pulverization of the alloy particle and corrosion/oxidation of La and Mg in alkaline electrolyte.

The La–Mg–Ni-based PuNi 3 -type La 0.7 Mg 0.3 Ni 2.55 - x Co 0.45 Cu x ( x = 0 , 0.1 , 0.2 , 0.3 , 0.4 ) hydrogen storage alloys were prepared by casting and rapid quenching. Ni in the alloy was partly substituted by Cu in order to improve the cycle stabilities of the alloys. The effects of the substitution of Cu for Ni on the microstructures and electrochemical performances of the as-cast and quenched alloys were investigated in detail. The results obtained by XRD, SEM and TEM show that the as-cast and quenched alloys have a multiphase structure which is composed of two main phases (La, Mg) Ni 3 and LaNi 5 as well as a residual phase LaNi 2 . The substitution of Cu for Ni leads to an obvious increase of the LaNi 2 phase in the as-cast alloys, and it also helps the formation of a desired amorphous phase in the as-quenched alloy. The results of the electrochemical measurement indicate that the substitution of Cu for Ni obviously decreases the discharge capacities of the as-cast and quenched alloys, but it significantly improves their cycle stabilities. The substitution of Cu for Ni slightly improves the discharge potential characteristics and the activation capabilities of the as-cast alloys, but it leads to reversal results for the as-quenched alloys.

The electrode alloys ( Mg 1 - x Zr x ) 2 Ni ( x = 0 , 0.1 ) were prepared by mechanical alloying (MA). Mg in the alloy was partially substituted with Zr in order to improve the electrochemical characteristics of the Mg 2 Ni -type alloy. The microstructures and the electrochemical characteristics of the experimental alloys were measured systemically. The effects of substituting Mg with Zr as well as the relevant MA technique on the microstructures and electrochemical performances of the alloys were investigated in detail. The results show that the substitution of Zr is favourable for the formation of an amorphous phase. The electrochemical measurement indicated that the substitution of Zr can dramatically enhance the discharge capacity and cycle stability, and it markedly improves the discharge voltage characteristic of the alloys. For a fixed alloy, the electrochemical performances, including the cycle stability, the discharge voltage characteristic and discharge capacity, of the alloys were significantly improved with the increase of the ball-milling duration.

In order to improve the electrochemical performances of La–Mg–Ni system (PuNi3-type) hydrogen storage alloy, a trace of B was added in La2Mg(Ni0.85Co0.15)9 alloy. La2Mg(Ni0.85Co0.15)9B x ( x = 0 , 0.05 , 0.1 , 0.15 , 0.2 ) hydrogen storage alloys were prepared by casting and rapid quenching. The electrochemical charging-discharging cycling lives and microstructures of the as-cast and quenched alloys were measured and analyzed. The effects of B additive on the microstructures and cycling lives of as-cast and quenched alloys were investigated in detail. The results show that the as-cast and quenched alloys are composed of the (La, Mg)Ni3 phase (PuNi3 structure), the LaNi5 phase and the LaNi2 phase. A trace of the Ni2B phase exists in the as-cast alloys containing B. The Ni2B phase in the alloys containing B nearly disappears after rapid quenching and the relative ratio of each phase in the alloys changes with the variety of the quenching rate. The addition of B obviously enhances the charging-discharging cycling stabilities of the as-cast and quenched alloys. When B content x increases from 0 to 0.2, the cycling lives of the as-cast and quenched at 20 m/s alloys were increased from 72 to 94 cycles and from 86 to 104 cycles, respectively.

The La–Mg–Ni-based (PuNi3-type) La2Mg(Ni0.85Co0.15)9 M x ( M = B , Cr, Ti; x = 0 , 0.1 ) hydrogen storage electrode alloys were prepared by casting and rapid quenching. The microstructures and electrochemical performances of the as-cast and quenched alloys were analyzed and measured. The effects of B, Cr, Ti and rapid quenching on the microstructures and electrochemical properties of the alloys were investigated in detail. The obtained results show that the as-cast and quenched alloys are composed of the (La, Mg)Ni3 phase (PuNi3-type structure) and the LaNi5 phase as well as the small amount of the LaNi2 phase. A trace of the Ni2B phase exists in the as-cast alloy containing boron, and the Ni2B phase in the alloy nearly disappears after rapid quenching. The relative amount of each phase in the alloys depends on the composition of the alloys and the quenching rate. The addition of B, Cr enhances the cycle stability of the as-cast alloys, while the addition of Ti reduces the cycle stability of the as-cast alloy. The addition of B, Cr, Ti decreases the discharge capacities of the alloys. Rapid quenching increase the cycle lives of the alloys, but the effect of rapid quenching on the discharge capacity of the alloys is different. Except the alloy containing boron, the capacities of the alloys decrease monotonously with the increase of the quenching rate. The capacity of the alloy containing boron has a maximum value with the increase of the quenching rate. The as-cast and quenched alloys have an excellent activation performance.

In order to compare the effects of the preparation techniques on the electrochemical performances of Co-free AB 5 -type hydrogen storage alloys, the Co-free AB 5 -type La x Mm 1 - x (NiMnSiAlFe) 4.9 ( x = 0 , 0.45 , 0.75 , 1.0 ) hydrogen storage alloys were prepared by casting and rapid quenching. The phase structures and microstructures of the as-cast and quenched alloys were analyzed by XRD, SEM and TEM. The effects of the rapid quenching on the microstructures and electrochemical performances of the specimen alloys were investigated in detail. The obtained results show that, when the amount of the La substitution x = 0.75 , the discharge capacity of the as-quenched alloy with quenching rate of 10 m/s is 292 mA h/g with charge-discharge current density of 60 mA/g, the capacity retaining rate ( R h ) is 61.2% after 300 charge-discharge cycles with current density of 300 mA/g. When the amount of the La substitution x = 1 , the discharge capacities of the as-quenched alloy with quenching rate of 10 and 16 m/s are 300 and 292 mA h/g, and the capacity retaining rates ( R h ) are 62.3% and 65.0%, respectively.