Performance improvement in direct borohydride/peroxide fuel cells

Direct borohydride/peroxide fuel cells (DBPFCs) show progressively deteriorating performance during operation for various reasons such as decreasing reactant concentrations, gas evolution and uneven distribution of liquids. The present study aims to emphasize the importance of certain design parameters, such as bipolar plate materials, flow fields and manifold design, in determining the DBPFC performance. Bipolar materials and flow channel design have been investigated. A power density of 67 mW cm^?2 has been obtained with composite graphite and parallel flow channel bipolar plates. It has increased to 87 mW cm^?2 using sintered graphite and then to 93.3 mW cm^?2 using sintered graphite with serpentine flow fields. The stacking of DBPFCs results in a loss of performance and unstable output. The performance has remained nearly unchanged as the cell number was increased by applying an independent cell liquid distribution network (ICLDN). Using an ICLDN, power densities of 98.3, 83.3 and 82 mW cm^?2 have been obtained for single-cell, 3-cell and 6-cell stacks, respectively. Finally, a controlled oxidant feeding system (COFS) has been developed to provide stable output power, and it has demonstrated a stable output power of 6 W for 2.5 h.     

A development of direct hydrazine/hydrogen peroxide fuel cell

A direct hydrazine fuel cell using H₂O₂ as the oxidizer has been developed. The N₂H₄/H₂O₂ fuel cell is assembled by using Ni-Pt/C composite catalyst as the anode catalyst, Au/C as the cathode catalyst, and Nafion membrane as the electrolyte. Both anolyte and catholyte show significant influences on cell voltage and cell performance. The open-circuit voltage of the N₂H₄/H₂O₂ fuel cell reaches up to 1.75 V when using alkaline N₂H₄ solution as the anolyte and acidic H₂O₂ solution as the catholyte. A maximum power density of 1.02 W cm⁻² has been achieved at operation temperature of 80 °C. The number of electrons exchanged in the H₂O₂ reduction reaction on Au/C catalyst is 2.     

Iron phthalocyanine as a cathode catalyst for a direct borohydride fuel cell

A direct borohydride fuel cell (DBFC) is constructed using a cathode based on iron phthalocyanine (FePc) catalyst supported on active carbon (AC), and a AB₅-type hydrogen storage alloy (MmNi_3.55Co_0.75Mn_0.4Al_0.3) was used as the anode catalyst. The electrochemical properties are investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), etc. methods. The electrochemical experiments show that FePc-catalyzed cathode not only exhibits considerable electrocatalytic activity for oxygen reduction in the BH₄⁻ solutions, but also the existence of BH₄⁻ ions has almost no negative influences on the discharge performances of the air-breathing cathode. At the optimum conditions of 6 M KOH + 0.8 M KBH₄ and room temperature, the maximal power density of 92 mW cm⁻² is obtained for this cell with a discharge current density of 175 mA cm⁻² at a cell voltage of 0.53 V. The new type alkaline fuel cell overcomes the problem of the conventional fuel cell in which both noble metal catalysts and expensive ion exchange membrane were used.     

Response to Disselkamp: Direct peroxide/peroxide fuel cell as a novel type fuel cell

Besides hydrogen peroxide is known as conventionally oxidizer, it is both a fuel and a source of ignition. Platinum is not suitable catalyst for oxidation and reduction of hydrogen peroxide, because it directly converts the hydrogen peroxide to oxygen gas. In this study, the oxidation mechanism of peroxide is investigated and a fuel cell operating with acidic peroxide as oxidant and basic peroxide as fuel is constructed. The peroxide oxidation reaction in novel alkaline direct peroxide/peroxide fuel cell (DPPFC), shown feasible here using less expensive carbon supported Nickel catalyst, makes the alkaline direct peroxide/peroxide fuel cell a potentially low cost technology compared to PEM fuel cell technology, which employs platinum catalysts. The power density of 3.75 mW cm⁻² at a cell voltage of 0.55 V and a current density of 14 mA cm⁻² was achieved in our fuel cell.     

Improving the direct borohydride fuel cell performance with thiourea as the additive in the sodium borohydride solution

In this study, the effects of the additive thiourea (TU) have been investigated under steady state/steady-flow and uniform state/uniform-flow systems with the aim of minimizing the anodic hydrogen evolution on Pd in order to increase the performance of a direct borohydride fuel cell. The fuel cell has consisted of Pd/C anode, Pt/C cathode and Na⁺ form Nafion membrane as the electrolyte. There has been a small improvement in peak power density and fuel utilization ratio by addition of TU (1.6 × 10⁻³ M) into the sodium borohydride solution; the peak power densities of 14.4 and 15.1 mW cm⁻², and fuel utilization ratios of 21.6% and 23.2% have been obtained without and with TU, respectively.     

Comparison of the electrochemical oxidation of borohydride and dimethylamine borane on platinum electrodes: Implication for direct fuel cells

The electrochemical behaviour of dimethylamine borane and borohydride on platinum electrodes was investigated by cyclic voltammetry and polarization curves in discharges processes. Several overlapping peaks appear in the domain of hydrogen oxidation, i.e., in the potential range of −1.25 V to −0.50 V versus Ag/AgCl, mainly with the borohydride. This behaviour is associated with the hydrolysis of BH₄⁻ or (CH₃)₂NHBH₃. As a consequence of secondary reactions the borohydride and dimethylamine borane oxidation in 3 M NaOH solution shows, respectively, a four- to six-electron process and a four- to five-electron process in direct fuel cells. The direct oxidation of the borohydride exhibits a peak at about −0.07 V versus Ag/AgCl, while the dimethylamine borane peak is at about −0.03 V versus Ag/AgCl. For the 0.04 M concentration the borohydride displays a power density of 31 W m⁻² which is 16% higher than that of the dimethylamine borane.     

Copper hexacyanoferrate as cathode material for hydrogen peroxide fuel cell

The current need for handheld electronic devices with high energy autonomy has amplified research into clean and mobile energy source developments. Among suitable and promising technologies for this application, fuel cells, FCs are highlighted because of their minimal emission of pollutants and high efficiency. One type of FCs that has yet to be studied is the hydrogen peroxide/direct hydrogen peroxide fuel cell (DPPFCs). The present work is dedicated to the development of DPPFCs of one compartment using copper hexacyanoferrates (CuHCFs) as cathodic material and a Ni grid as anodic material. CuHCFs containing Fe^II and/or Fe^III were synthesized, characterized and their electrocatalyst performances were compared in 0.1 mol L⁻¹ HCl and 0.5 mol L⁻¹ H₂O₂. The maximum power densities reached for the CuFe^II was 8.3 mW cm⁻² and for the CuFe^IIFe^III was 2.9 mW cm⁻². The CuHCFs cathode materials show promising results, standing out as innovative materials for such an application.     

Agni-catalyzed anode for direct borohydride fuel cells

Ag and AgNi powders were comparatively tested as anodic catalysts for direct electrochemical oxidation of borohydride. Discharge experiments demonstrated for the first time that both Ag and AgNi electrode can catalyze the electrooxidation of borohydride, delivering a high capacity of >7e$>7\mathrm{e}$ oxidation for a borohydride ion. In comparison, AgNi-catalyzed borohydride fuel cells exhibited a higher discharge voltage and capacity, possibly due to a combined action of the electrocatalytic activity of Ni component for borohydride electrooxidation and the depression of borohydride hydrolysis by Ag atoms.     

Enhanced performance of direct peroxide/peroxide fuel cell by using ultrafine Nickel Ferric Ferrocyanide nanoparticles as the cathode catalyst

Direct peroxide-peroxide fuel cell (DPPFC) employing with H₂O₂ both as the fuel and oxidant is an attractive fuel cell due to its no intermediates, easy handling, low toxicity and expense. However, the major gap of DPPFC is the cathode performance as a result of the slow reaction kinetics of H₂O₂ electro-reduction and thus the target issue is to design cathode catalysts with high performance and low cost. Herein, different with using noble metal of state-of-the-art, we have successfully synthesized ultra-fine NiFe ferrocyanide (NiFeHCF) nanoparticles (the mean particles size is 2.5 nm) through a co-precipitation method, which is used as the cathode catalyst towards H₂O₂ reduction in acidic medium. The current density of H₂O₂ reduction on the resultant NiFeHCF electrode after the 1800 s test period at ?0.1, 0 and 0.1 V are 121, 93 and 76 mA cm², respectively. Meanwhile, a single two-compartment DPPFC cell with NiFeHCF nanoparticles as the cathode and Ni/Ni foam as the anode is assembled and displayed a stable OCP of 1.09 V and a peak power density of 36 mW cm^?2 at 20 °C, which is much higher than that of a DPPFC employed with Pd nano-catalyst as cathode.     

Study of fuel efficiency in a direct borohydride fuel cell

In this study, direct borohydride fuel cells (DBFCs) potentialities are evaluated. These emerging systems make it possible to reach maximum powers of about 200 mW cm⁻² at room temperature and ambient air (natural convection) with high concentrated borohydride solutions. On the other hand, a part of borohydride hydrolyses during cell operating which leads to hydrogen formation and fuel loss: the practical capacity represents about only 18% of the theoretical one. In order to improve fuel efficiency, thiourea is tested as an inhibitor of the catalytic hydrolysis associated with BH₄⁻ electro-oxidation on Pt. The practical capacity is drastically improved: it represents about 64% of the theoretical one. Against, electrochemical performances (I–E curves) are affected by the presence of thiourea.     

A direct borohydride fuel cell employing Prussian Blue as mediated electron-transfer hydrogen peroxide reduction catalyst

A direct borohydride-hydrogen peroxide fuel cell employing carbon-supported Prussian Blue (PB) as mediated electron-transfer cathode catalyst is reported. While operating at 30 °C, the direct borohydride-hydrogen peroxide fuel cell employing carbon-supported PB cathode catalyst shows superior performance with the maximum output power density of 68 mW cm⁻² at an operating voltage of 1.1 V compared to direct borohydride-hydrogen peroxide fuel cell employing the conventional gold-based cathode with the maximum output power density of 47 mW cm⁻² at an operating voltage of 0.7 V. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy Dispersive X-ray Analysis (EDAX) suggest that anchoring of Cetyl-Trimethyl Ammonium Bromide (CTAB) as a surfactant moiety on carbon-supported PB affects the catalyst morphology. Polarization studies on direct borohydride-hydrogen peroxide fuel cell with carbon-supported CTAB-anchored PB cathode exhibit better performance with the maximum output power density of 50 mW cm⁻² at an operating voltage of 1 V than the direct borohydride-hydrogen peroxide fuel cell with carbon-supported Prussian Blue without CTAB with the maximum output power density of 29 mW cm⁻² at an operating voltage of 1 V.     

Investigation of PtNi/C anode electrocatalysts for direct borohydride fuel cell

In this study, carbon-supported PtNi alloys with different molar ratios synthesized by borohydride reduction were evaluated as anode catalysts for sodium borohydride fuel cells. The higher angle shifts of the Pt peaks from X-ray diffraction (XRD) account for the alloy formation between Pt and Ni. The negative shift of Pt 4f XPS spectrum for PtNi(7:3)/C also indicates an electronic structural change of Pt in the alloyed PtNi/C catalyst. The cyclic voltammetry (CV) results show that the PtNi(x:10 − x)/C catalysts are electrochemically active toward borohydride oxidation at the potential range between −0.6 V and +0.1 V vs. Hg/HgO electrode, and PtNi(7:3)/C presents the strongest peak current density among three catalysts with different molar ratios. The results of amperometric i–t curves (i–t) tests also show that the steady-state current density is the highest on PtNi(7:3)/C among alloy catalysts. The higher electrocatalytic activity of the PtNi(7:3)/C can be attributed to the alloy effect and the Pt electronic structure change due to the addition of Ni.     

Cathode electrocatalyst selection and deposition for a direct borohydride/hydrogen peroxide fuel cell

Catalyst selection, deposition method and substrate material selection are essential aspects for the design of efficient electrodes for fuel cells. Research is described to identify a potential catalyst for hydrogen peroxide reduction, an effective catalyst deposition method, and supporting material for a direct borohydride/hydrogen peroxide fuel cell. Several conclusions are reached. Using Pourbaix diagrams to guide experimental testing, gold is identified as an effective catalyst which minimizes gas evolution of hydrogen peroxide while providing high power density. Activated carbon cloth which features high surface area and high microporosity is found to be well suited for the supporting material for catalyst deposition. Electrodeposition and plasma sputtering deposition methods are compared to conventional techniques for depositing gold on diffusion layers. Both methods provide much higher power densities than the conventional method. The sputtering method however allows a much lower catalyst loading and well-dispersed deposits of nanoscale particles. Using these techniques, a peak power density of 680 mW cm⁻² is achieved at 60 °C with a direct borohydride/hydrogen peroxide fuel cell which employs palladium as the anode catalyst and gold as the cathode catalyst.     

Direct borohydride fuel cell using Ni-based composite anodes

In this study, nickel-based composite anode catalysts consisting of Ni with either Pd on carbon or Pt on carbon (the ratio of Ni:Pd or Ni:Pt being 25:1) were prepared for use in direct borohydride fuel cells (DBFCs). Cathode catalysts used were 1 mg cm⁻² Pt/C or Pd electrodeposited on activated carbon cloth. The oxidants were oxygen, oxygen in air, or acidified hydrogen peroxide. Alkaline solution of sodium borohydride was used as fuel in the cell. High power performance has been achieved by DBFC using non-precious metal, Ni-based composite anodes with relatively low anodic loading (e.g., 270 mW cm⁻² for NaBH₄/O₂ fuel cell at 60 °C, 665 mW cm⁻² for NaBH₄/H₂O₂ fuel cell at 60 °C). Effects of temperature, oxidant, and anode catalyst loading on the DBFC performance were investigated. The cell was operated for about 100 h and its performance stability was recorded.     

High activity of Au-Cu/C electrocatalyst as anodic catalyst for direct borohydride-hydrogen peroxide fuel cell

Carbon supported Au-Cu bimetallic nanoparticles are prepared by a modified NaBH₄ reduction method in aqueous solution at room temperature. The electrocatalytic activities of the Au-Cu/C catalysts are investigated by cyclic voltammetry, chronoamperometry, chronopotentiometry and fuel cell experiments. It has been found that the Au-Cu/C catalysts have much higher catalytic activity for the direct oxidation of BH₄⁻ than Au/C catalyst. Especially, the Au₆₇Cu₃₃/C catalyst presents the highest catalytic activity for BH₄⁻ electrooxidation among all as-prepared catalysts, and the DBHFC using Au₆₇Cu₃₃/C anode catalyst and Au/C cathode catalyst shows the maximum power density of 51.8 mW cm⁻² at 69.5 mA cm⁻² and 20 °C.     

Performance of an alkaline direct ethanol fuel cell with hydrogen peroxide as oxidant

An alkaline direct ethanol fuel cell (DEFC) with hydrogen peroxide as the oxidant is developed and tested. The present fuel cell consists of a non-platinum anode, an anion exchange membrane, and a non-platinum cathode. It is demonstrated that the peak power density of the fuel cell is 130 mW cm⁻² at 60 °C (160 mW cm⁻² at 80 °C), which is 44% higher than that of the same fuel cell setup but with oxygen as the oxidant. The improved performance as compared with the fuel cell with oxygen as the oxidant is mainly attributed to the superior electrochemical kinetics of the hydrogen peroxide reduction reaction and the reduced ohmic loss associated with the liquid oxidant.     

A three-dimensional two-phase flow model for a liquid-fed direct methanol fuel cell

A three-dimensional, two-phase, multi-component model has been developed for a liquid-fed DMFC. The modeling domain consists of the membrane, two catalyst layers, two diffusion layers, and two channels. Both liquid and gas phases are considered in the entire anode, including the channel, the diffusion layer and the catalyst layer; while at the cathode, two phases are considered in the gas diffusion layer and the catalyst layer but only single gas phase is considered in the channels. For electrochemical kinetics, the Tafel equation incorporating the effects of two phases is used at both the cathode and anode sides. At the anode side the presence of gas phase reduces the active catalyst areas, while at the cathode side the presence of liquid water reduces the active catalyst areas. The mixed potential effects due to methanol crossover are also included in the model. The results from the two-phase flow mode fit the experimental results better than those from the single-phase model. The modeling results show that the single-phase models over-predict methanol crossover. The modeling results also show that the porosity of the anode diffusion layer plays an important role in the DMFC performance. With low diffusion layer porosity, the produced carbon dioxide cannot be removed effectively from the catalyst layer, thus reducing the active catalyst area as well as blocking methanol from reaching the reaction zone. A similar effect exits in the cathode for the liquid water.     

Influences of sodium borohydride concentration on direct borohydride fuel cell performance

In this work, the effects of sodium borohydride concentration on the performance of direct borohydride fuel cell, which consisted of Pd/C anode, Pt/C cathode and Na⁺ form Nafion^® membrane as the electrolyte, have been investigated in steady state/steady-flow and uniform state/uniform-flow systems. The experimental results have revealed that the power density increased as the sodium borohydride concentration increased in the SSSF system. Peak power densities of 7.1, 10.1 and 11.7 mW cm⁻² have been obtained at 0.5, 1 and 1.5 M, respectively. However, the performance has decreased when the sodium borohydride concentration has been increased, and the fuel utilization ratios of 29.8%, 21.6% and 20.4% have been obtained at 0.5, 1 and 1.5 M, respectively in the USUF system.     

Influence of operation conditions on direct NaBH4/H2O2 fuel cell performance

Although hydrogen fuel cells have attracted so much attentions in these years because of the application prospect in electric vehicles, some obstacles have not been solved yet, among which hydrogen storage is one of the biggest. Direct borohydride fuel cell (DBFC) is another choice without hydrogen storage problem because borohydride is used as reactant directly in the fuel cell. In this paper, DBFC performance under different operation conditions was studied including electrolyte membrane type, operation temperature, borohydride concentration, supporting electrolyte and oxidant. Results showed that, with Pt/C and MnO₂ as anode and cathode electrocatalyst, respectively, Nafion^® 117 membrane as electrolyte, 1.0 M, 3.0 M and 6.0 M NaBH₄ and H₂O₂ solution in NaOH as reactant solution, 80 °C operation, the peak power density could reach 130 mW/cm².     

Cobalt nickel boride nanocomposite as high-performance anode catalyst for direct borohydride fuel cell

Similar to MXene, MAB is a group of 2D ceramic/metallic boride materials which exhibits unique properties for various applications. However, these 2D sheets tend to stack and therefore lose their active surface area and functions. Herein, an amorphous cobalt nickel boride (Co–Ni–B) nanocomposite is prepared with a combination of 2D sheets and nanoparticles in the center to avoid agglomeration. This unique structure holds the 2D nano-sheets with massive surface area which contains numerous catalytic active sites. This nanocomposite is prepared as an electrocatalyst for borohydride electrooxidation reaction (BOR). It shows outstanding catalytic activity through improving the kinetic parameters of BH₄^? oxidation, owing to abundant ultrathin 2D structure on the surface, which provide free interspace and electroactive sites for charge/mass transport. The anode catalyst led to a 209 mW/cm² maximum power density with high open circuit potential of 1.06 V at room temperature in a miniature direct borohydride fuel cell (DBFC). It also showed a great longevity of up to 45 h at an output power density of 64 mW/cm², which is higher than the Co–B, Ni–B and PtRu/C. The cost reduction and prospective scale-up production of the Co–Ni–B catalyst are also addressed.