Direct Borohydride-hydrogen Peroxide Fuel Cell Research Articles

High-performance direct borohydride-hydrogen peroxide fuel cell using Ni foam-supported Ni-Co nanoparticles as a noble-metal free anode electrocatalyst

The Ni-Co nanoparticles with various Ni/Co ratios are immobilized on a Ni foam (NF) template, coated with reduced graphene oxides (rGO), and used as a novel noble-metal-free anode electrocatalyst for enhanced performance direct borohydride fuel cells. The electrochemical active surface area (EASA) of Ni50Co50 /rGO/NF (1515 cm2) catalyst is 45.5 times larger than NF (33.3 cm2). A comprehensive study of direct borohydride-hydrogen peroxide fuel cell (DBHPFC) by Pt/C (0.5 mg cm−2) as a cathode and Ni50-Co50/rGO/NF as an anode is accomplished, so an open-circuit potential (OCP) of 1.90 V and the maximum power density of 309 mW cm−2 is obtained at 60 ◦C. These results show that electrocatalyst Ni50Co50/rGO/NF is a suitable candidate for use as an electrocatalyst in DBHPFC due to its low cost, ease of synthesis, excellent structural stability, and high catalytic performance.

Synergistic enhancement of oxygen vacancy enrichment and morphology regulation in CeO2-NiCo2O4 heterostructure catalysts for high-performance cathodes in direct borohydride-hydrogen peroxide fuel cells

Hydrogen peroxide (H2O2) emerges as a viable oxidant for fuel cells, necessitating the development of an efficient and cost-effective electrocatalyst for the hydrogen peroxide reduction reaction (HPRR). In this study, we synthesized a self-supporting, highly active HPRR electrocatalyst comprising two morphologically distinct components: CeO2-NiCo2O4 nanowires and CeO2-NiCo2O4 metal organic framework derivatives, via a two-step hydrothermal process followed by air calcination. X-ray diffraction and transmission electron microscopy analysis confirmed the presence of CeO2 and NiCo2O4, revealing the amalgamated interface between them. CeO2 exhibits multifunctionality in regulating the surface electronic configuration of NiCo2O4, fostering synergistic connections, and introducing oxygen deficiencies to enhance the catalytic efficacy in HPRR. Electrochemical measurements demonstrate a reduction current density of 789.9 mA·cm−2 at −0.8 V vs. Ag/AgCl. The assembly of direct borohydride-hydrogen peroxide fuel cell (DBHPFC) exhibits a peak power density of 45.2 mW·cm−2, demonstrating durable stability over a continuous operation period of 120 h. This investigation providing evidence that the fabrication of heterostructured catalysts based on CeO2 for HPRR is a viable approach for the development of high-efficiency electrocatalysts in fuel cell technology.

Co‑MOF-Derived Flake-Like Co3O4 Supported Pd Nanoparticles as High-Performance Hydrogen Peroxide Electroreduction Catalysts

Development of highly efficient catalysts for the hydrogen peroxide reduction reaction (HPRR) has been a focus of research for fuel cells using hydrogen peroxide (H2O2) as an alternative cathode oxidant. The carbon-doped flake-like cobalt oxide electrode (Co3O4@C NF) was prepared on nickel foam (NF) by annealing the metal organic framework (MOF). A Co3O4@C/Pd NF (CPNF) electrode was derived from Co3O4@C NF by supporting Pd nanoparticles. Half-cell tests demonstrated that the CPNF electrode exhibited outstanding catalytic performance. The CPNF electrode displayed a high current density of 932 mA cm−2 at −0.8 V (vs Ag/AgCl). This aligns with its low activation energy (7392.8 J mol−1). The electron transfer numbers for the Co3O4@C NF and CPNF electrodes were 2.97 and 3.32, respectively. Incorporating CPNF as the cathode of Direct borohydride-hydrogen peroxide fuel cell (DBHPFC) yielded notable catalytic performance, with a peak power density of 68 mW cm−2. The CPNF electrode exhibited remarkable stability, sustaining continuous current discharge for over 20 h. These electrochemical properties result from the structural characteristics obtained through MOF annealing, which increases the number of exposed active sites and enhances ion transport. Therefore, CPNF stands as a promising cathode catalyst for DBHPFC.

Bipolar Membranes for Direct Borohydride Fuel Cells-A Review.

Direct liquid fuel cells (DLFCs) operate directly on liquid fuel instead of hydrogen, as in proton-exchange membrane fuel cells. DLFCs have the advantages of higher energy densities and fewer issues with the transportation and storage of their fuels compared with compressed hydrogen and are adapted to mobile applications. Among DLFCs, the direct borohydride-hydrogen peroxide fuel cell (DBPFC) is one of the most promising liquid fuel cell technologies. DBPFCs are fed sodium borohydride (NaBH4) as the fuel and hydrogen peroxide (H2O2) as the oxidant. Introducing H2O2 as the oxidant brings further advantages to DBPFC regarding higher theoretical cell voltage (3.01 V) than typical direct borohydride fuel cells operating on oxygen (1.64 V). The present review examines different membrane types for use in borohydride fuel cells, particularly emphasizing the importance of using bipolar membranes (BPMs). The combination of a cation-exchange membrane (CEM) and anion-exchange membrane (AEM) in the structure of BPMs makes them ideal for DBPFCs. BPMs maintain the required pH gradient between the alkaline NaBH4 anolyte and the acidic H2O2 catholyte, efficiently preventing the crossover of the involved species. This review highlights the vast potential application of BPMs and the need for ongoing research and development in DBPFCs. This will allow for fully realizing the significance of BPMs and their potential application, as there is still not enough published research in the field.

Effect of anode conditions on the performance of direct borohydride–hydrogen peroxide fuel cell system

Direct borohydride–hydrogen peroxide fuel cells (DBHPFCs) are attractive power sources for space applications. Although the cathode conditions are known to affect the system performance, the effect of the anode conditions is rarely investigated. Thus, in this study, a DBHPFC system was tested under various anode conditions, such as electrocatalyst, fuel concentration, and stabilizer concentration, to investigate their effects on the system performance. A virtual DBHPFC system was analyzed based on the experimental data obtained from fuel cell tests. The anode electrocatalyst had a considerable effect on the mass and electrochemical reaction rate of the fuel cell system, but had minimal effect on the decomposition reaction rate. The NaBH4 concentration greatly influenced the mass and decomposition reaction rate of the fuel cell system; however, it had minimal impact on the electrochemical reaction rate. The NaOH concentration affected the electrochemical reaction rate, decomposition reaction rate, and mass of the fuel cell system. Therefore, the significant effects of the anode conditions on the electrochemical reaction rate, decomposition reaction rate, and mass of the fuel cell system prompt the need for their careful selection through fuel cell tests and system analysis.

Ag–Ni nanoparticles supported on multiwalled carbon nanotubes as a cathode electrocatalyst for direct borohydride–hydrogen peroxide fuel cells

In this study, an Ag–Ni electrocatalyst supported on multiwalled carbon nanotubes (MWCNTs) was investigated to develop a new type of cathode electrocatalyst for direct borohydride–hydrogen peroxide fuel cells (DBHPFCs). Monometallic electrocatalysts consisting of Au, Ag, or Ni have previously demonstrated relatively high catalytic activity and selectivity. The characteristics of each catalyst (Au/MWCNTs, Ag/MWCNTs, and Ni/MWCNTs) were determined through various techniques, such as scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray diffraction; additionally, their performance was evaluated using a fuel cell test. Based on the results, Ag and Ni were selected to construct a bimetallic electrocatalyst, owing to their relatively superior catalytic selectivity at high current densities. Ag–Ni/MWCNT catalysts with various atomic percentage ratios were prepared, and their characteristics were investigated. Among the bimetallic electrocatalysts, Ag41Ni59/MWCNTs exhibited the highest maximum power density. Furthermore, Ag41Ni59/MWCNTs exhibited good catalytic selectivity even at high operating temperatures. The prepared Ag–Ni bimetallic electrocatalyst has moderate catalytic activity and selectivity and is more cost effective than Au and Ag catalysts; therefore, it can be used as a new type of cathode electrocatalyst for DBHPFCs.

High-Performance Direct Borohydride-Hydrogen Peroxide Fuel Cell Using Ni Foam-Supported Ni-Co Nanoparticles as a Noble-Metal Free Anode Electrocatalyst

High-Performance Direct Borohydride-Hydrogen Peroxide Fuel Cell Using Ni Foam-Supported Ni-Co Nanoparticles as a Noble-Metal Free Anode Electrocatalyst

Effect of cathode conditions on performance of direct borohydride–hydrogen peroxide fuel cell system for space exploration

Fuel cell tests are conducted under various cathode conditions to investigate the effect of cathode conditions on the performance of a direct borohydride–hydrogen peroxide fuel cell (DBHPFC) system. The efficiency and mass of the virtual DBHPFC system are estimated based on experimental data obtained from the fuel cell tests. The type of cathode electrocatalyst considerably affects the performance and mass of the fuel cell system. Ni is the most suitable for the cathode owing to its high fuel utilization efficiency and low cost. The H2O2 concentration has a minimal effect on the performance of the fuel cell system but considerably affects the mass of the fuel cell system. The mass of the fuel cell system negatively correlates with the H2O2 concentration. The H3PO4 concentration and operating temperature have a negligible effect on the performance and mass of the fuel cell system; 5 wt% H3PO4 is sufficient to suppress the decomposition reaction and improve the fuel cell performance. Operation at room temperature is recommended for high fuel utilization efficiency. The decomposition reaction rate affects the efficiency and mass of the DBHPFC system. Consequently, the decomposition and electrochemical reaction rates should be considered when determining suitable cathode conditions for the DBHPFC system.

Gold-based bimetallic electrocatalysts supported on multiwalled carbon nanotubes for direct borohydride–hydrogen peroxide fuel cell

Au-based bimetallic electrocatalysts supported on multiwalled carbon nanotubes (MWCNTs) were investigated to improve the selectivity and activity of the catalysts for direct borohydride–hydrogen peroxide fuel cells (DBPFCs). Au–Pd and Au–Ni catalysts were used as the anode and cathode catalysts, respectively. The Au-based bimetallic catalysts with various atomic percentage ratios were investigated using inductively coupled plasma optical emission spectroscopy, transmission electron microscopy, Brunauer–Emmett–Teller analysis, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and fuel cell tests. Among the Au-based bimetallic catalysts, Au49Pd51/MWCNTs was found to be the most suitable for the anode and Au74Ni26/MWCNTs was the most suitable for the cathode. The effects of the operating temperature and operation time on the catalytic selectivity and activity were also investigated to evaluate the performance of the bimetallic catalysts. It was found that the Au-based bimetallic catalysts had good catalytic selectivity and activity even at an elevated operating temperature and a maximum power density of 279.5 mW/cm2 was obtained at 52.0 ± 2.0 °C when Au49Pd51/MWCNTs (anode) and Au74Ni26/MWCNTs (cathode) were used for the DBPFC electrodes. It was also found that the Au-based bimetallic catalysts showed stable performance for 70 min. Thus, the Au-based bimetallic catalysts can be widely used for DBPFCs.

Reduced graphene oxide foam supported CoNi nanosheets as an efficient anode catalyst for direct borohydride hydrogen peroxide fuel cell

Abstract Catalytic performance and NaBH4 utilization are two crucial concerns in the electrooxidation of NaBH4. To improve the inherent properties of regular performance and low fuel utilization of the transition metal Co and Ni, an efficient anode catalyst of ultra-thin CoNi nanosheets modified novel 3D self-supported reduced graphene oxide foam is prepared in this work. The alkaline condition borohydride oxidation reaction on the prepared catalyst is investigated in a typical three-electrode system. The prepared catalyst shows a high performance due to the large electrochemical active surface area, low activation energy (8.29 kJ·mol−1), and the small electrochemical impedance it embraced. Linear scan voltammetry recorded in a low concentration of NaBH4 suggests that borohydride oxidation is a first-order reaction on the prepared catalyst. Based on the unique structure of the catalyst, which is useful to capture the hydrogen and perform further oxidation of hydrogen, higher utilization of NaBH4 achieved on the catalyst. Besides, the prepared anode catalyst applied to a direct borohydride-hydrogen peroxide fuel cell (DBHPFC). The results of polarization curve and power density curves, as well as stability research, all indicate that the as-prepared catalyst is a highly efficient anode material for application in DBHPFC.

Novel self-supported reduced graphene oxide foam-based CoAu electrode: An original anode catalyst for electrooxidation of borohydride in borohydride fuel cell

An original three-dimensional self-supported reduced graphene oxide (rGO) foam is successfully prepared in this work. This novel support material, modified with Co nanosheets and Au nanoparticles, is employed as a high-performance catalyst for NaBH4 electrooxidation under alkaline condition. The surface chemical component and morphology of the catalyst is characterized by X-ray diffraction pattern, X-ray photoelectron spectroscopy, scanning electron microscope. The synthesized electrode exhibits excellent performance (1.35 A cm−2 at 0 V) towards NaBH4 electrooxidation. The unique structure of rGO foam caused a large electrochemical active surface area (EASA(Au) = 390 m2 g−1), low electrochemical impedance, as well as 55.4% utilization efficiency of NaBH4. Also, catalytic kinetic parameters during the electrooxidation reaction of NaBH4 in a low NaBH4 concentration are investigated. Results indicate that oxidation of BH4− is a first-order reaction, and the exchanged number of electrons obtained at the CoAu/rGO foam electrode is 6.9. Finally, we practically apply it to a direct borohydride-hydrogen peroxide fuel cell (DBHPFC). This work suggests that the prepared rGO foam is an excellent current collector, and CoAu/rGO foam electrode is a promising anode catalyst to apply in DBHPFC.

A Novel Anode for Direct Borohydride-Hydrogen Peroxide Fuel Cell: Au Nanoparticles Decorated 3D Self-Supported Reduced Graphene Oxide Foam

A novel anode material of Au nanoparticles grown on a self-supported reduced graphene oxide foam is successfully fabricated in this work. Characterization methods like X-ray diffraction pattern, sc...

Nitrogen-Doped Carbon Catalysts Modified with Au-M (M = Co, Ni, Cu) Nanoparticles As the Anode Material for Direct Borohydride-Hydrogen Peroxide Fuel Cells

Direct borohydride-hydrogen peroxide fuel cells (DBHPFCs) have several advantages such as high theoretical cell voltage (2.11-3.02 V), high energy density (12-17 kWh kg-1) and, finally, no CO poisoning during their operation. Therefore, anode material is the key factor for complete direct oxidation of borohydride. This study is focused on the synthesis of the nitrogen-doped carbon (N-doped C) catalysts supported Au-M (M = Co, Ni, Cu) nanoparticles using a rapid microwave heating method with the aim to use them as the anode material for DBHPFC. The electrocatalytic activity of the prepared M/N-doped C and Au-M/N-doped C catalysts for the borohydride oxidation reaction (BOR) was evaluated using cyclic voltammetry and chronoamperometry. The direct borohydride-hydrogen peroxide fuel cell was assembled using Pt as the cathode and the prepared M/N-doped C and Au-M/N-doped C catalysts as the anodes. The performance of a DBHPFC operating with 1 M NaBH4 + 4 M NaOH as fuel and 5 M H2O2 + 1.5 M HCl as an oxidant was investigated at different temperatures. It has been determined that the prepared Au-M/N-doped C catalysts have а higher activity and а better stability for the oxidation of borohydride compared to those of M/N-doped C (M = Co, Ni, Cu) catalysts. The direct borohydride-hydrogen peroxide fuel cell exhibited an open circuit voltage of cа. 1.8 V when the Au-M/N-doped C catalysts were assembled as the anodes.

Smooth and Fiber-Shaped Co Coatings Decorated with Pt Crystallites As the Anode Catalysts for Direct Borohydride-Hydrogen Peroxide Fuel Cells

In the present work, the smooth and fiber-shaped Co coatings decorated with Pt crystallites were investigated as the anode material in direct borohydride-hydrogen peroxide fuel cells (DBHPFCs). The Co sublayers, which have different structures, e.g. smooth and fiber-shaped, were used as a substrate for the depositing of Pt crystallites. The Co layer having smooth structure was deposited on the Cu surface (denoted as Cosmooth/Cu) via electroless deposition using morpholine borane as a reducing agent. Co layers, which have a fiber-shaped structure and the thickness of ~3 mm, were electroplated on the Cu surface (denoted as Cofiber/Cu) from the electrolyte containing CoSO4, NaOH and N-(2-Hydroxyethyl) ethylenediamine. The Pt crystallites were deposited on the Cosmooth/Cu and Cofiber/Cu electrodes by their immersion into a Pt(IV)-containing solution at a temperature of 25oC for different time periods. It has been determined that the Pt loadings were in the range from 10 to 14 µgPt cm–2 and 5 to 29 µgPt cm–2 in the PtCosmooth/Cu and PtCofiber/Cu catalysts, respectively. The activity of the prepared PtCosmooth/Cu and PtCofiber/Cu catalysts for borohydride oxidation reaction (BOR) was evaluated using cyclic voltammetry and chronoamperometry. The performance of a DBHPFC operating with 1 M NaBH4 + 4 M NaOH as fuel and 5 M H2O2 + 1.5 M HCl as an oxidant, while employing Pt as the cathode catalyst and PtCosmooth/Cu and PtCofiber/Cu catalysts with different Pt loadings as the anodes were investigated. It has been determined that the prepаred PtCosmooth/Cu and PtCofiber/Cu cаtаlysts hаve а higher аctivity аnd а better stаbility for the oxidаtion of BH4 - compаred to those of Cosmooth/Cu аnd Cofiber/Cu. The аssembled direct borohydride-hydrogen peroxide fuel cell with PtCosmooth/Cu and PtCofiber/Cu cаtаlysts as the anodes exhibited аn open circuit voltаge of cа. 1.9 V. Acknowledgment This research was funded by a grant (No. M-ERA.NET-1/2016) from the Research Council of Lithuania.

Preparation of Pt/G and PtNi/G nanocatalysts with high electrocatalytic activity for borohydride oxidation and investigation of different operation condition on the performance of direct borohydride-hydrogen peroxide fuel cell

In this work, graphene supported Pt (Pt/G) and NiPt nanoparticles (NiPt/G) were synthesized by in situ chemical reduction of graphene oxide, Ni+2 and Pt+4 ions. The structural investigation was performed by Fourier transform infrared (FT-IR) spectra, X-ray photoelectron spectroscopy (XPS), Brunauer, Emmett, and Teller (BET) analysis, Field emission scanning electron microscopy (FE-SEM), Energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The electrocatalytic activity of the Pt/G and PtNi/G catalysts toward BH4− oxidation in alkaline media was investigated by means of cyclic voltammetry (CV) and chronoamperometry (CA). The results showed that the catalytic activity of the PtNi/G catalyst toward NaBH4 electrooxidation was higher than that of Pt/G because of the synergistic effect between Pt and Ni. A direct borohydride-hydrogen peroxide fuel cell (DBHPFC) was fabricated using Pt/G (0.5 mg cm−2) as cathode catalyst and NiPt/G as anode catalyst. The maximum power density was 64.9 mW cm−2 at 60 °C, 1 M NaBH4 and 2 M H2O2 for anodic loading of 2 mg cm−2 and 60.4 mW cm−2 at 60 °C, 1 M NaBH4 and 2 M H2O2 for anodic loading of 1mg cm−2.

Improvement of energy conversion efficiency and power generation in direct borohydride-hydrogen peroxide fuel cell: The effect of Ni-M core-shell nanoparticles (M = Pt, Pd, Ru)/Multiwalled Carbon Nanotubes on the cell performance

In this study, core@shell nanoparticles with Ni as a core material and Pt, Pd and Ru as shell materials are synthesized on multiwalled carbon nanotube (MWCNT) as catalyst support using the sequence reduction method. The influence of Ni@Pt, Ni@Pd and Ni@Ru core@shell nanoparticles on MWCNT toward borohydride oxidation in alkaline solution is investigated by various three-electrode electrochemical techniques. Also, the impact of these anodic electrocatalysts on the performance of direct borohydride-hydrogen peroxide fuel cell (DBHPFC) is evaluated. The structural and morphological properties of electrocatalysts are studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). The results of three electrode investigations show that Ni@Pd/MWCNT has excellent catalytic activity since borohydride oxidation current density on Ni@Pd/MWCNT (34773.27 A g−1) is 1.37 and 9.19 times higher than those of Ni@Pt/MWCNT (25347.27 A g−1) and Ni@Ru/MWCNT (3782.83 A g−1), respectively. Also, the energy conversion efficiency and power density of DBHPFC with Ni@Pd/MWCNT (246.82 mW cm−2) increase to 34.27% and 51.53% respect to Ni@Pt/MWCNT (162.24 mW cm−2) and Ni@Ru/MWCNT (119.62 mW cm−2), respectively. This study reveals that Ni@Pd/MWCNT has highest activity toward borohydride oxidation and stability in fuel cell.

Carbon supported Ni1Pt1 nanocatalyst as superior electrocatalyst with increased power density in direct borohydride-hydrogen peroxide and investigation of cell impedance at different temperatures and discharging currents

Carbon supported NiPt and Pt nanoparticles are synthesized using chemical reduction with sodium borohydride (NaBH4). The metal loading in synthesized nanocatalysts was 20 wt% and the ratio of Ni:Pt in the nanocatalysts was 1:1. The physical properties of nanocatalysts are investigated by Field Emission scanning electron microscopy (FE-SEM), energy-dispersive x-ray spectroscopy (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The electrocatalytic activity of the NiPt/C and Pt/C catalysts toward BH4− oxidation in alkaline media is investigated by means of cyclic voltammetry (CV), chronopotentiometry (CP), chronoamperometry (CA). The current densities are normalized respect to actual Pt loading in the nanocatalysts. Cyclic voltammograms show that the NiPt/C electrocatalyst has higher catalytic activity toward NaBH4 electrooxidation. A direct borohydride-hydrogen peroxide fuel cell (DBHPFC) is fabricated using Pt/C (0.5 mg cm−2) as cathodic catalyst and NiPt/C (1 mg cm−2) as anodic catalyst. The influence of cell temperature, sodium borohydride and hydrogen peroxide concentration on the I-V and I-P curves is investigated. The obtained maximum power density is 106.63 mW cm−2 at 60 °C, 1 M NaBH4 and 2 M H2O2. Impedance spectrums are taken in NaBH4 1 M + H2O2 2 M. The impedance results show that with increasing temperature and discharging current, anodic and cathodic charge transfer resistance reduce.

Pd nanoparticles support on rGO-C@TiC coaxial nanowires as a novel 3D electrode for NaBH4 electrooxidation

Recently, direct borohydride fuel cell (DBFC) has been considering as a promising energy conversion devices. During the development of DBFC, reducing the use of noble metals and increasing the anode performance are the hot topic in recent researches. In this article, reduced graphene oxide nanosheets deposit on C@TiC coaxial nanowire array (rGO-C@TiC) by means of a combine method of chemical vapor deposition and electrodeposition is chosen as 3D current collector for Pd nanoparticles deposition. The morphology and crystal structure of the as-obtained 3D electrode is checked with FESEM, TEM, EDS, and XRD. Results claim that the as-prepared 3D electrode exhibits a mushroom-like structure with the mean diameter size of Pd is 5.32 nm. Their catalytic ability for NaBH4 electro-oxidation is evaluated in a three electrode system by using the method of cycle voltammetry and chronoamperometry, proving that the 3D Pd-rGO-C@TiC electrode has a higher catalytic performance. The oxidation current density of 1.35 A cm−2 mg−1Pd is achieved at −0.6 V. Furthermore, a direct borohydride-hydrogen peroxide fuel cell (DBHPFC) is assembled by using the as-prepared Pd-rGO-C@TiC electrode and a Pd/CFC electrode as anode and cathode catalyst, respectively, and a maximum power density of 68.5 mW cm−2 is obtained. In addition, the assembled DBHPFC shows excellent higher performance based on the mass activity basis (1427.1 W g−1) among those reported literatures, indicating that our Pd-rGO-C@TiC could be acted as a promising cost-effective and ponderable alternative catalyst for NaBH4 electrooxidation.

Design specifications of direct borohydride–hydrogen peroxide fuel cell system for space missions

The design specifications of a direct borohydride–hydrogen peroxide fuel cell (DBPFC) system for space missions were determined based on the energy density. A unit cell test of the DBPFC with electrocatalysts supported on multiwalled carbon nanotubes was conducted to evaluate the DBPFC performance. A relationship between the current density and voltage was obtained from the test results to estimate the total mass and energy density of the DBPFC system. The effects of changing the voltage efficiency and fuel concentrations on the total mass of the DBPFC system were investigated to determine the appropriate design specifications for space missions. When the voltage efficiency was 35%, the system mass was the lowest, regardless of the fuel concentrations. Finally, the energy density of the DBPFC system operating at the optimum voltage efficiency was calculated at various fuel concentrations. When the NaBH4 and H2O2 concentrations are higher than 20 and 65 wt%, respectively, the energy density (>400 Wh/kg) of the DBPFC system is higher than those of other power sources and the DBPFC system can be widely used for space missions.

Investigation of carbon-supported Ni@Ag core-shell nanoparticles as electrocatalyst for electrooxidation of sodium borohydride

Carbon-supported Ni@Ag core-shell nanoparticles were synthesized and used as the anode electrocatalyst for direct borohydride-hydrogen peroxide fuel cell (DBHFC). The morphology, structure, and composition of the as-prepared electrocatalysts are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). Electrochemical characterizations are performed by cyclic voltammetry (CV), chronoamperometry (CA), linear scan voltammetry with rotating disk electrode (LSV RDE), and fuel cell test. The catalytic behaviors and main kinetic parameters (e.g., Tafel slope, number of electrons exchanged, exchange current density, and apparent activation energy) toward BH4‐ oxidation on Ag/C and Ni@Ag/C electrocatalysts are determined. Results show that the as-prepared nanoparticles have a core-shell structure with the average size approximately 13 nm. The kinetics of NaBH4 oxidation is faster for Ni@Ag/C than that for Ag/C. Among the as-prepared catalysts, the highest transition electron value and the lowest apparent activation energy are obtained on Ni1@Ag1/C; the values are 4.8 and 20.23 kJ mol−1, respectively. The DBHFC using Ni1@Ag1/C as anode electrocatalyst and Pt mesh (1 cm2) as cathode electrode obtains the maximum anodic power density as high as 8.54 mW cm−2 at a discharge current density of 8.42 mA cm−2 at 25 °C.