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Abstract: The performance stability of the direct borohydride fuel cell (DBFC) working under passive conditions was studied in this work. The stability within hours was found to be greatly affected by mass transport properties of different cell components. It was significantly improved by modifying electrode structures, increasing hydrophobicity of the cathode and using pretreated membranes. On the other hand, the stability of the DBFC cell for more than 100h was determined by the durabilities of these cell components. The nickel anode and silver cathode were found to degrade after prolonged operations and thus the durabilities of these non-noble metal catalysts need to be improved. [Copyright &y& Elsevier]

Abstract: Borohydrides, a group of compounds with large hydrogen contents, can generate hydrogen readily by their hydrolysis reaction. In this study catalysts based on nickel and cobalt were developed to accelerate the hydrolysis reaction for hydrogen generation. Catalysts in four forms were tested for each metal: fine metal powder, metal salt, metal boride and Raney metal. It was found that the hydrolysis reaction was primary a zero-order reaction under the catalysis of these catalysts. Although cobalt showed higher catalytic activity than nickel in most cases, Raney Ni exhibited almost the same activity as the Raney Co. Among four chemical forms for nickel, Raney Ni demonstrated the best performance. Moreover, Raney catalysts made from alloys of nickel and cobalt showed even higher activity. The reaction on Raney metals was also characterized by a slowdown in hydrogen generation rate at low borohydride concentrations because of a mass transfer limitation. [Copyright &y& Elsevier]

Abstract: It has been reported that sodium (potassium) borohydride can be formed by reaction of sodium (potassium) borate with Mg and hydrogen or magnesium hydride. However, few investigations on reaction mechanism have been reported. Here, we studied the NaBH4 formation mechanism of Mg+NaBO2 +2H2 =NaBH4 +MgO through morphology observations, structure and micro composition analyses. It was found that when heating the reactor to 400°C, NaBO2 particles were agglomerated with Mg particles and a NaBO2 network was formed due to the sintering effect. With further heating the reactor, a porous product layer (composed of NaBH4 and MgO) was formed on Mg particles. It was found that no matter whether Mg was hydrogenated or not, Mg could react with sodium borate and hydrogen to form sodium borohydride. Elevating the reaction temperature was of benefit to NaBH4 formation. Higher NaBH4 yield can be obtained by using partially hydrogenated then dehydrogenated Mg. [Copyright &y& Elsevier]

A fuel cell was assembled using alkaline borohydride solutions as the fuel. The specific gravity, specific viscosity, and melting points of the borohydride solutions were evaluated. With increasing the NaBH4 concentration, the specific gravity was decreased but the viscosity was increased consistently. The effects of NaBH4 and NaOH concentrations on the cell and electrode polarizations were investigated. The increase of NaBH4 concentration improved the anode performance a little but obviously increased the cathode polarization due to the BH4− crossover. As a result, the cell polarization increased when using high concentrated borohydride solutions. According to the Nernst’s equation, the increase of NaOH concentration is favorable to the anode, but negative to the cathode polarization. In principle, the cell polarization has nothing to do with the NaOH concentration according to the cell reaction NaBH4+O2=NaBO2+2H2O. However, the experimental results showed that the high concentration of NaOH aggravated the cell polarization at higher current densities. [Copyright &y& Elsevier]

Based on three chemical states of hydrogen: protide (H−), protium (H0) and proton (H+), a triangular hydrogen energy system was proposed. The transfers among protide, protium and proton attracted our attention. We experimentally proved that NaBH4 as a protide carrier can release its energy through a fuel cell (borohydride fuel cell) directly or generate hydrogen gas for polymer electrolyte membrane fuel cell application. The used fuel (meta-borate) can be reverted to NaBH4 through a reaction with a saline hydride (MgH2). [Copyright &y& Elsevier]

A convenient method was developed to synthesize NaBH4 by the reaction of MgH2 with Na2B4O7 through ball milling at room temperature. In order to improve the sodium borohydride yield, Na compounds were added to compensate the Na insufficiency in reactants when MgH2 instead of NaH was used as the reducing agent. It was found that Na2CO3 addition was better than NaOH or Na2O2 addition in increasing the borohydride yield. [Copyright &y& Elsevier]