Selective Borohydride Oxidation Reactions of Zeolitic Imidazolate Framework-Derived Bimetallic Carbon Alloy Electrocatalysts for Alkaline Fuel Cell Applications

Abstract

Direct borohydride fuel cells are a particular class of alkaline direct liquid fuel cells that show interesting performances for mobile applications owing to the use of sodium borohydride (NaBH4) as fuel. The complete electrooxidation of NaBH4 proceeds via an eight-electron pathway. However, due to the inevitable hydrolysis of borohydride at the electrode, the released electrons are usually less than 8. The use of anode catalysts with good performance and high utilization of BH4 – is therefore imperative for practical applications. In this work, we report the development of an anode catalyst derived from trimetallic zeolitic imidazolate framework (ZIF) with M–N x active centers. The trimetallic ZIF precursor (FeCoZn-ZIF) was derived by the codoping of Fe and Co on ZIF-8 synthesized through a fast, aqueous synthesis under ambient conditions. Subsequently, carbonization yielded a carbon alloy catalyst (FeCo-ZNC) with enhanced porosity. The nanotubular structure of the formed carbon assisted in faster electron transport, and the oxidation current density of FeCo-ZNC reached 56.5 mA cm–2 at 0.61 V during electrocatalytic NaBH4 oxidation under alkaline conditions. The enhanced electrocatalytic performance induced by the morphological and textural features of FeCo-ZNC along with active reaction centers such as pyridinic N, graphitic N, and Co–N x enabled NaBH4 electrooxidation via an eight-electron transfer, indicating its potential as a promising catalyst for borohydride oxidation reactions (BORs).

Research progress on direct borohydride fuel cells

“…Since the end of the last century, there have been many investigations on anode catalysts of the DBFC. [66][67][68][69][70][71][72][73][74][75][76][77][78] Among these catalyst materials, the platinum group metal catalysts (such as platinum and palladium) have been usually applied as efficient electrocatalysts for BOR due to their outstanding adsorption capacity to BH 4…”

“…Since the end of the last century, there have been many investigations on anode catalysts of the DBFC. 66–78 Among these catalyst materials, the platinum group metal catalysts (such as platinum and palladium) have been usually applied as efficient electrocatalysts for BOR due to their outstanding adsorption capacity to BH 4 − . For example, Braesch et al investigated the production of hydrogen and intermediates during BOR to compare the catalytic abilities of Pd, Pt and Au, 57 thus finding Pd was the most promising electrode with superior catalytic ability, as well as hydrogen absorption capacity.…”

Controllable Electrochemical Liberation of Hydrogen from Sodium Borohydride

“…Generally, NaBH 4 is relatively stable in alkaline solution at pH>12 [7] . In alkaline media, NaBH 4 electrooxidation reaction (BOR) is as follow: [8] $$$\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr {\rm BH}{_{4}}{^{- }}+{\rm 8OH}{^{- }}\rightarrow {\rm BO}{_{2}}{^{- }}+{\rm 6H}{_{2}}{\rm O}+{\rm 8e}{^{- }}\hfill\cr}}$$$ $$$\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr E{^{{\rm \theta} }}=- 1.24\mskip4mu {\rm V}\ {\rm vs}.\ {\rm SHE}\hfill\cr}}$$$ …”

Controllable Electrochemical Liberation of Hydrogen from Sodium Borohydride

“…Generally, NaBH 4 is relatively stable in alkaline solution at pH>12 [7] . In alkaline media, NaBH 4 electrooxidation reaction (BOR) is as follow: [8] $$$\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr {\rm BH}{_{4}}{^{- }}+{\rm 8OH}{^{- }}\rightarrow {\rm BO}{_{2}}{^{- }}+{\rm 6H}{_{2}}{\rm O}+{\rm 8e}{^{- }}\hfill\cr}}$$$ $$$\vcenter{\openup.5em\halign{$\displaystyle{#}$\cr E{^{{\rm \theta} }}=- 1.24\mskip4mu {\rm V}\ {\rm vs}.\ {\rm SHE}\hfill\cr}}$$$ …”

“…Generally, NaBH 4 is relatively stable in alkaline solution at pH > 12. [7] In alkaline media, NaBH 4 electrooxidation reaction (BOR) is as follow: [8] BH 4…”