A Thin‐Film Direct Hydrogen Peroxide/Borohydride Micro Fuel Cell

Abstract

The rapid development of miniature devices (e.g., microsensors) [ 1 ] has resulted in an increasing demand for miniature power sources. For example, microfuel cells, [2][3][4][5][6][7] microbatteries, [ 8 ] and microsolar cells [ 9 ] have been considered as possible on-chip power sources. This paper proposes a novel design for a microfuel cell as an on-chip power source and demonstrates its fabrication and operation to prove the concept. The design of the on-chip cell concurrently realizes a high operating voltage of 1.6 V, and high power. Its simple design is important from the viewpoints of fabrication (e.g., replication), integration, and compatibility with other microdevices.Fuel cells that directly convert chemical energy into electricity with high effi ciency attract considerable research attention. [10][11][12][13][14] All such fuel cells involve the couplings of cathode/ anode, reduction/oxidation reactions, charge movement (electron-transfer/ion-transfer), and often reactions in either acid or alkaline electrolyte. During operation, cathodic fuel is reduced (i.e., gains electrons) and anodic fuel is oxidized (i.e., looses electrons) simultaneously. The potential difference between the cathode and anode results in the generation of current where electrons move from anode to cathode in the external circuit and ions move in the electrolyte. Depending on the acid (C H + )/ alkaline(C OH-) concentration in the electrolyte, fuel cells can be described as being either acidic (C H + > C OH-≈ 0) or alkaline (C OH-> C H + ≈ 0). Because the stable potential window of water (H 2 O) is only about 1.23 V at various pH values, the measured cell voltage of these developed fuel cells is around 1 V which is lower than 1.23V.Direct borohydride fuel cells (DBFCs) have attracted increasing attention since their demonstration by Amendola et al. in 1999, [ 15 ] and more recently considerable efforts have been made to further improve their performance. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] In principle, DBFCs can only work in an alkaline electrolyte because borohydride is unstable in neutral and acidic media. [ 18 , 20 ] Accordingly, conventional DBFCs use a single alkaline electrolyte for both the anode and the cathode. Although the theoretical cell voltage of conventional DBFCs (with a single alkaline electrolyte for both the anode and the cathode) is 1.64 V, the measured cell voltage at open-circuit conditions of these cells is only around 1 V, which is also because the stable potential window of water is only 1.23 V. However, the reduction potential of cathodic fuel (e.g. O 2 , H 2 O 2 , etc.) is much lower in alkaline medium when compared with that in acidic medium. If the reduction of cathodic fuel (O 2 or H 2 O 2 ) in an acid electrolyte can be coupled with oxidization of anodic fuel (BH 4 − ) in an alkaline electrolyte, the DBFC would exhibit much higher operating voltage. This should be an interesting topic and a great challenge because one fuel cell can not contain both acidelectrolyte and a...

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