A study on performance stability of the passive direct borohydride fuel cell

doi:10.1016/j.jpowsour.2008.08.063

Journal of Power Sources

Volume 185, Issue 2, 1 December 2008, Pages 1257-1261

https://doi.org/10.1016/j.jpowsour.2008.08.063 Get rights and content

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 100 h 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.

Introduction

Worldwide concern on energy security and environment pollution has stimulated the rapid development of fuel cell technologies. However, commercialization of hydrogen fuel cells has to overcome several obstacles including high cost and hydrogen storage. As an efficient and cost-effective system has not yet been established to produce, store and transport hydrogen, it is hoped that developments of direct liquid fuel cells could circumvent the hydrogen storage problem. In view of fuel energy density, cell performance and fuel safety, the direct borohydride fuel cell (DBFC) is a very promising liquid fuel cell [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21]. It generates power according to the following reaction:BH₄⁻ + 8OH⁻ = BO₂⁻ + 6H₂O + 8e⁻

The DBFC offers higher cell voltage than hydrogen fuel cells. Development of the DBFC is currently focused on improving power density and fuel efficiency [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21]. By optimizing electrode compositions and structures for both the anode and cathode, the power density of the DBFC has been increased to 250 mW cm⁻² at temperatures around 60 °C [15], or higher than 100 mW cm⁻² at room temperature in passive cells [20]. Fuel efficiency could also be improved by using Au or Au alloys [1], [3], [13], employing bi-metallic anode catalysts [15], [20], or adding some agents like thiourea to depress hydrogen evolution [3], [17], [20].

Besides power density, performance stability is another important property in DBFC development. A good initial performance does not guarantee a stable and repeatable performance over a long operation. But in practical applications, it is essential to achieve reliable and repeatable cell performance. The direct borohydride fuel cell differs from hydrogen fuel cells in many aspects due to their different chemistries. Many factors were found to influence performance stability of the DBFC. In this study, we report our efforts in improving performance stability of the passive DBFC by adjusting electrode or cell structure, and modifying cell materials. The results would help understanding electrochemical and mass transport processes in the DBFC configuration and inspire further DBFC developments.

Section snippets

Experimental details

The anodes of the DBFCs were prepared by first mixing and grinding nickel powder (INCO Inc., type 210) with polytetrafluoroethylene (PTFE) powder at a weight ratio of 1:0.05 in a mortar, and then filling the formed paste into a piece of nickel foam. The Ni catalyst loading was 0.2 g cm⁻². The cathodes were prepared by spreading carbon supported Pt or Ag catalysts (Pt 30 wt% or Ag 20 wt% on Vulcan XC-72 from E-Tek Corp.) on Toray carbon paper TGP-H-060. The catalyst loading of the cathodes was Pt 1 mg

Results and discussion

It is desirable for the DBFC to demonstrate stable output during prolonged power generation. For the cell with definite fuel volume (30 ml in this work), it is hoped that the cell voltage could keep stable until NaBH₄ in the fuel is near exhaustion. Also the performance could be repeatable after the refueling. In this research, we divided the performance stability of DBFC into short-term and long-term stability. While short-term stability refers to performance stability within hours during

Conclusions

In order to develop the direct borohydride fuel cell into a viable technology, the effects influencing its performance stability were studied in this research. The stability of the DBFC cell within hours was found to be greatly affected by the mass transport properties of different cell components. The porosities of the anode and cathode supporting materials, the membrane pretreatment and borohydride concentration had significant influences on performance stability. By modifying the structures

Acknowledgement

This work was partially supported by National Hi-tech projects 863 of China under the contract nos. 2006AA05Z120 and 2007AA05Z144.

References (23)

S.C. Amendola et al.
J. Power Sources
(1999)
E. Gyenge
Electrochim. Acta
(2004)
B.H. Liu et al.
Electrochim. Acta
(2005)
A. Verma et al.
J. Power Sources
(2005)
N.A. Choudhury et al.
J. Power Sources
(2005)
R.X. Feng et al.
Electrochem. Commun.
(2005)
C.P. de Leon et al.
J. Power Sources
(2006)
J.H. Wee
J. Power Sources
(2006)
B.H. Liu et al.
Electrochim. Acta
(2004)
H. Cheng et al.
J. Power Sources
(2006)

H. Cheng et al.

J. Membr. Sci.

(2007)

Cited by (16)

Effects of power control techniques on hydrogen and oxygen evolution in direct borohydride peroxide fuel cells
2017, International Journal of Hydrogen Energy
Citation Excerpt :
Higher initial concentrations lead to a faster rate of hydrogen evolution. Hydrogen evolution at a constant potential decreases with time, which depends on the borohydride concentration in the solution [16]. Yamazaki et al. investigated the peroxide reduction and showed a decrease in the oxygen evolution rate in the following order: Ag > Pd > Pt >> Au > Ni.
Direct borohydride/peroxide fuel cells (DBPFCs) have some attractive features, such as high energy density, high theoretical cell power and low operational temperature. The drawbacks that cause performance loss include low efficiency and security challenges. Hydrogen and oxygen evolutions are major issues that should be considered when stacking a DBPFC. These gas evolutions significantly affect the DBPFC performance, efficiency and security. However, the gases were also produced in the case of an open circuit potential and depend on the applied voltage and current. Therefore, in the present study, the effects of cell loading on gas evolution were investigated. The DBPFC was operated under a constant voltage of 1.2 V and controlled using the maximum peak power tracking (MPPT) method. The MPPT control provided higher power generation and higher hydrogen evolution than observed using the constant voltage mode.
Transport phenomena in direct borohydride fuel cells
2017, Applied Energy
Citation Excerpt :
Hence, it is critically important to alleviate the water flooding problem. Typically, there are two operation modes for the oxygen delivery to the reaction sites: active mode [108,109] and passive mode [110–113]. In passive fuel cells, oxygen is transported to the cathode CL by diffusion and natural convection, while the water removal from the cathode relies on passive forces, such as capillary forces.
Direct borohydride fuel cells, which convert the chemical energy stored in borohydride directly into electricity, are one of the most promising energy-conversion devices for portable, mobile and stationary power applications, primarily because they run on a carbon-free fuel and uses the low-cost materials. For this reason, this energy technology has undergone a rapid progress over the last decade. This article provides a comprehensive review of transport phenomena of various species in direct borohydride fuel cells. Particular attention is paid to the understanding of the critical issues related to transportation of various species through the fuel cell structure.
Enhancement of electrocatalytic performance of hydrogen storage alloys by multi-walled carbon nanotubes for sodium borohydride oxidation
2014, Journal of Power Sources
Catalytic electrodes consisting of MmNi_0.58Co_0.07Mn_0.04Al_0.02 (AB₅-type alloy) and multi-walled carbon nanotubes (MWNTs) are studied for NaBH₄ electrooxidation and are characterized by scanning electron microscope and X-ray diffractometer. The NaBH₄ electrooxidation performance on the AB₅/MWNTs electrode is tested by cyclic voltammetry and chronoamperometry methods. The electrode performance is significantly affected by the content of MWNTs and the optimized content of MWNTs is found to be 2 wt.%. The steady state current density for NaBH₄ electrooxidation at the AB₅/MWNTs (2 wt.%) electrode is about twice of that at the AB₅ electrode without MWNTs. The utilization efficiency of NaBH₄ at the AB₅/MWNTs electrode is 61.5% higher than that at the pristine AB₅ electrode. The enhanced electrocatalytic activity and NaBH₄ utilization at the AB₅/MWNTs (2 wt.%) electrode can be attributed to MWNTs, which acts as a hydrogen adsorbent to diminish hydrogen release.
Effect of electrode fabrication method and substrate material on performance of alkaline fuel cells
2013, Electrochemistry Communications
Citation Excerpt :
The relation of hydrogen evolution rate with the anode current on a Pd catalyst is dependent on the concentration of borohydride [6]. Nickel foam was used as substrate of liquid fuel diffusion layer or electrode substrate in borohydride fuel cells [12–18]. It should be noted that Ni foam is made of nickel which is catalytically active towards both borohydride electrooxidation and hydrolysis.
Performance of an electrode is influenced by electrode fabrication method and electrode substrate. In this study, different anodes were prepared by either electron beam physical vapor deposition or ink paste method, using Ni foam or carbon paper as electrode substrate. These electrodes were tested in an alkaline fuel cell using borohydride as the fuel. A nanoscale palladium thin film anode prepared by physical vapor deposition delivered power performance close to that of an ink pasted electrode with a much higher catalyst loading. Ni foam as electrode substrate demonstrated a higher power performance and yet a lower efficiency than carbon paper. Ni foam alone was used as anode and achieved a peak power density of 174 m Wcm^− 2 at 60 °C. Thus, nickel foam had both positive effect (e.g. electrooxidation of NaBH₄) and negative effect (e.g. hydrolysis) on the fuel cell performance.
Sodium borohydride as a fuel for the future
2011, Renewable and Sustainable Energy Reviews
Citation Excerpt :
It is also very high when compared to the methanol, formic acid, and hydrazine systems, with theoretical cell voltages of 1.19, 1.45 and 1.56 V, respectively. The performance of fuel cells that operate on NaBH4 as the fuel and oxygen or hydrogen peroxide (H2O2) as oxidants has been investigated in several laboratories [253,433,486,515–619]. Although the initial suggestion of using NaBH4 as an anodic fuel dates from 1962 [433], there was a hiatus of almost 40 years until the idea deserved a renewed interest.
In a time of unprecedented change in environmental, geopolitical and socio-economic world affairs, the search for new energy materials has become a topic of great relevance. Sodium borohydride, NaBH₄, seems to be a promising fuel in the context of the future hydrogen economy. NaBH₄ belongs to a class of materials with the highest gravimetric hydrogen densities, which has been discovered in the 1940s by Schlesinger and Brown. In the present paper, the most relevant issues concerning the use of NaBH₄ are examined. Its basic properties are summarised and its synthesis methods are described. The general processes of NaBH₄ oxidation, hydrolysis, and monitoring are reviewed. A comprehensive bibliometric analysis of the NaBH₄ publications in the energy field opens the discussion for current perspectives and future outlook of NaBH₄ as an efficient energy/hydrogen carrier. Despite the observed exponential increase in the research on NaBH₄ it is clear that further efforts are still necessary for achieving significant overchanges.
High performance polymer chemical hydrogel-based electrode binder materials for direct borohydride fuel cells
2011, Journal of Power Sources
Citation Excerpt :
The same technique of MEA fabrication was adopted by Liu et al. [36], who opined that it is useful to leave some space between the anode and the membrane so that the fuel being in liquid state would be able to reach the anode easily and also the release of hydrogen evolved by decomposition/hydrolysis of BH4− fuel would be facilitated. Liu et al. [37] observed that in a DBFC performance stability test, the cell using an anode tightly pressed onto the membrane exhibited a quick decrease of cell voltage as compared to the cell wherein the anode was loosely pressed onto the membrane. Kim et al. [38] remarked that since the fuel and Na+ ions can easily transfer through the liquid medium, a close contact between the anode and the membrane is not necessary.
Novel, cost-effective, high-performance, and environment-friendly electrode binders, comprising polyvinyl alcohol chemical hydrogel (PCH) and chitosan chemical hydrogel (CCH), are reported for direct borohydride fuel cells (DBFCs). PCH and CCH binders-based electrodes have been fabricated using a novel, simple, cost-effective, time-effective, and environmentally benign technique. Morphologies and electrochemical performance in DBFCs of the chemical hydrogel binder-based electrodes have been compared with those of Nafion^® binder-based electrodes. Relationships between the performance of binders in DBFCs with structural features of the polymers and the polymer-based chemical hydrogels are discussed. The CCH binder exhibited better performance than a Nafion^® binder whereas the PCH binder exhibited comparable performance to Nafion^® in DBFCs operating at elevated cell temperatures. The better performance of CCH binder at higher operating cell temperatures has been ascribed to the hydrophilic nature and water retention characteristics of chitosan. DBFCs employing CCH binder-based electrodes and a Nafion^®-117 membrane as an electrolyte exhibited a maximum peak power density of about 589 mW cm⁻² at 70 °C.

View all citing articles on Scopus

View full text

Short communicationA study on performance stability of the passive direct borohydride fuel cell

Abstract

Introduction

Section snippets

Experimental details

Results and discussion

Conclusions

Acknowledgement

J. Power Sources

Electrochim. Acta

Electrochim. Acta

J. Power Sources

J. Power Sources

Electrochem. Commun.

J. Power Sources

J. Power Sources

Electrochim. Acta

J. Power Sources

J. Membr. Sci.

Short communication
A study on performance stability of the passive direct borohydride fuel cell