WO2013082211A1

WO2013082211A1 - Systems and methods for performing in situ measurements

Info

Publication number: WO2013082211A1
Application number: PCT/US2012/066940
Authority: WO
Inventors: Dawn A. Bonnell; Stephen S. Nonnenmann
Original assignee: The Trustees Of The University Of Pennsylvania
Priority date: 2011-11-29
Filing date: 2012-11-29
Publication date: 2013-06-06

Abstract

Systems and methods for performing in situ measurements of a fuel cell are disclosed. One such system comprises a housing, a frame, and a heater. The housing defines gas inlets, gas outlets, and a measurement port. The frame is positioned within the housing. The frame is adapted to secure the fuel cell in such a position that at least one of the gas inlets and at least one of the gas outlets are positioned on each side of the cell. The frame positions the fuel cell such that at least a portion of the fuel cell is accessible via the measurement port. The heater is positioned within the housing. The heater is operable to heat the fuel cell to a predetermined temperature. One such method comprises securing the fuel cell within the housing, heating the fuel cell to a predetermined temperature, and scanning the fuel cell through the measurement port.

Description

SYSTEMS AND METHODS FOR PERFORMING IN SITU MEASUREMENTS

FIELD OF THE INVENTION

The present invention is directed generally to measurement systems, and more particularly, to systems and methods for performing in situ measurement of fuel cell materials.

BACKGROUND OF THE INVENTION

In recent years, rapidly growing energy concerns have led to intense studies and testing relating to developments in energy-producing systems, and particularly, fuel cell technologies. Conventional fuel cells generate electricity directly from conversion of fuels such as natural gas or hydrogen via an electrochemical process.

In conventional fuel cells, elevated operating temperatures are necessary to maintain an effective electrochemical conversion process. For example, current solid oxide fuel cell (SOFC) technologies possess operating temperatures in a range of approximately 400-1000°C. With such high operating temperatures, it may be difficult to adequately test these fuel cells under operating conditions. Accordingly, improved systems and methods are desired for performing localized in situ measurements of fuel cell materials.

SUMMARY OF THE INVENTION

Aspects of the present invention are directed to systems and methods for performing in situ measurements.

In accordance with one aspect of the present invention, a system for performing in situ measurements of a fuel cell is disclosed. The system comprises a housing, a frame, and a heater. The housing defines a plurality of gas inlets, a plurality of gas outlets, and a measurement port. The frame is positioned within the housing. The frame is adapted to secure a fuel cell within the housing in such a position that at least one of the plurality of gas inlets and at least one of the plurality of gas outlets are positioned on each side of the fuel cell. The frame positions the fuel cell such that at least a portion of the fuel cell is accessible via the measurement port. The heater is positioned within the housing. The heater is operable to heat the fuel cell to a predetermined temperature.

In accordance with another aspect of the present invention, a method for performing in situ measurements of a fuel cell is disclosed. The method comprises securing the fuel cell to be measured within a housing, the housing defining a plurality of gas inlets, a plurality of gas outlets, and a measurement port such that at least one of the plurality of gas inlets and at least one of the plurality of gas outlets is positioned on each side of the fuel cell and at least a portion of the fuel cell is accessible via the measurement port; heating the fuel cell to a predetermined temperature; and scanning the fuel cell through the measurement port.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed description when read in connection with the accompanying drawings, with like elements having the same reference numerals. When a plurality of similar elements are present, a single reference numeral may be assigned to the plurality of similar elements with a small letter designation referring to specific elements. When referring to the elements collectively or to a non-specific one or more of the elements, the small letter designation may be dropped. According to common practice, the various features of the drawings are not drawn to scale unless otherwise indicated. To the contrary, the dimensions of the various features may be expanded or reduced for clarity. Included in the drawings are the following figures:

FIG. 1A is a diagram illustrating an exploded view of an exemplary system for performing in situ measurements in accordance with aspects of the present invention;

FIG. IB is a diagram illustrating a perspective view of the exemplary system of FIG. 1A;

FIG. 1C is a diagram illustrating a measurement operation of the exemplary system of FIG. 1A;

FIG. ID is a diagram illustrating an exemplary divider of the exemplary system of FIG. 1A; and

FIG. 2 is a flowchart illustrating an exemplary method for performing in situ measurements in accordance with aspects of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In order to optimize fuel cell materials, structure, and performance, it is desirable to experimentally observe electrochemical phenomena at the

electrode/electrolyte interface during operation of the fuel cells. Accordingly, the embodiments of the invention described herein relate to performing measurements of fuel cells in situ, i.e., at operating temperatures and in a gaseous environment. While the embodiments of the present invention are described herein with respect to the measurement of fuel cell materials, it will be understood that the invention is not so limited. The exemplary systems and methods described herein may be usable to test any number of materials that are desired to be tested at high temperatures, as would be understood by one of ordinary skill in the art from the description herein.

The systems and methods described herein generally utilize a miniature reaction chamber for use with a corresponding measurement device. The miniature reaction chamber is configured to isolate fuel cell material from the surrounding ambient environment at operating conditions (e.g., temperature, gas environment). The chamber may allow for separate fuel input to either electrode of the fuel cell in a vertical geometry, making measurements of a fuel cell (under operation) in cross- section feasible. Spatially resolved mapping of the conductive regimes across the electrolyte demonstrate the effectiveness of the exemplary system design.

The exemplary embodiments described herein allow for separate control of the fuel cell environment on either side of a given sample, e.g. by using (i) two or more different gas inlets, (ii) a controlled heater to adjust and maintain operating temperatures, and (iii) electrically-addressable feedthroughs for collection of electrical properties of the fuel cell. The single narrow port for the measurement device enables only the sample to be exposed to the environment outside the system, and not the entire interior of the housing. Therefore, the exemplary embodiments described herein enable a user to employ standard measurement devices with little or no modification, rather than purchase a separate, more customized (and expensive) measurement device to conduct the necessary experiments.

One suitable measurement device for use with the above-described reaction chamber is the atomic force microscope. Atomic force microscopy (AFM) utilizes an extremely sharp tip to scan a given material system under constant feedback, thus obtaining highly localized information on the surface, which includes but is not limited to topographic, dissipative, and mechanical properties. If the AFM tip is conductive, studies may expand to include the collection of highly localized and spatially resolved images of surface potential, current, and electrostatic forces, as well as AC properties such as impedance. Conductive AFM techniques (cAFM) may be implemented to resolve electrochemical phenomena, aqueous domains, and proton conduction.

Referring now to the drawings, FIGS. 1A-1D illustrates an exemplary system 100 for performing in situ measurements in accordance with aspects of the present invention. System 100 may be used to test fuel cell materials under operating conditions. As a general overview, system 100 includes a housing 110, a frame 130, and a heater 150. Additional details of system 100 are described herein. Housing 110 is configured to house the sample to be measured. As illustrated in FIGS. 1A and IB, housing defines a plurality of gas inlets 112a, 112b, a plurality of gas outlets 114a, 114b, and a measurement port 116. Gas inlets 112a, 112b and gas outlets 114a, 114b are usable to provide a gas to the interior of housing 110, e.g., in order to operate a fuel cell within housing 110. Measurement port 116 are usable to measure the sample within housing 110, e.g., using an atomic force microscope. Housing 110 may further include a plurality of electrical connections 118a, 118b and a heater connection 120, as shown in FIG. 1A. Electrical connections 118a, 118b are usable to provide an electrical signal to the sample within housing 110, e.g., wires/electrodes for providing a voltage bias across a fuel cell. Electrical connections 118a, 118b may also be usable to collect current produced by a fuel cell during operation within system 100. Heater connection 120 is usable to control and/or select a temperature for the interior of housing 110, e.g., a signal wire for controlling the heater to simulate operating conditions for a fuel cell. It will be understood that the number of inlets, outlets, and connections shown in FIGS. 1A and IB is for the purpose of illustration, and is not intended to be limiting. For example, housing 110 may have any number of gas and/or electrical connections as necessary to simulate the operation of the sample to be measured.

Housing 110 is configured to house the sample to be measured under operating conditions. Accordingly, housing 110 may be configured to accommodate high temperatures therein. Suitable materials for use in forming housing 110 include, for example, stainless steel. Other suitable materials will be known to one of ordinary skill in the art from the description herein.

In an exemplary embodiment, housing 110 has an approximately cylindrical shape, as shown in FIG. 1A. Housing 110 is enclosed by a lid 122, which forms an axial surface of housing 110. Lid 122 is connected to the remainder of housing 110 in such a way as to maintain the operating conditions within housing 110. For example, lid 122 may be connected to the remainder of housing 122 via a plurality of screws 124, as shown in FIG. IB. As will be further explained herein, measurement port 116 is defined in lid 122. It will be understood by one of ordinary skill in the art that the size and shape of housing 110 may be selected based on the size of the sample to be measured by system 100.

Housing 110 may also include a cap (not shown). Cap may be configured to cover the measurement port 116 to prevent leakage of gas from within housing 110. The cap may be specially design to substantially prevent exposing the interior of housing 110 to the external environment, while accommodating a probe from the measurement device, to enable measurement and/or scanning of the sample. The cap may be integrated with the lid 122 assembly in order to secure the sample and ensure proper gas flow. Further, the cap may be loaded between positioned between lid 122 and frame 130, and/or be integrally formed with lid 122 or frame 130.

As shown in FIG. 1A, housing 110 is sized to accommodate only a single sample (or fuel cell) therewithin. This may be desirably in order to easily maintain testing/operating conditions within housing 110. However, it will be understood that housing 110 may be made larger to accommodate multiple samples, as desired.

The interior of housing 110 may desirably be coated with a chemical sealant around each of the inlets and connections, and around the interface between lid 122 and the remainder of housing 110. This may be desirably to minimize leakage of gas from the interior of housing 110. Suitable high-temperature chemical sealants include, for example, those provided by Deacon Industries, located in Washington, Pennsylvania, USA.

Frame 130 is positioned within housing 110. Frame 130 is adapted to secure the sample to be measured within housing 110. Frame 130 may secure the sample in place, for example, by friction fit. Other mechanisms for securing the sample with frame 130 will be known to one of ordinary skill in the art from the description herein.

Frame 130 secures the sample in such a position that at least one of the plurality of gas inlets 112a, 112b and at least one of the plurality of gas outlets 114a, 114b is positioned on each side of the sample, as shown in FIG. 1A. Further, frame 130 secures the sample in such a position that at least a portion of the sample is accessible (e.g., able to be viewed, scanned, contacted) via measurement port 116. When the sample is secured by the frame, measurement port 116 has a field of view including a cross-section of the sample. It may be desirable that frame 130 secures the sample in such a position that measurement port 116 has a field of view including only a cross-section of the sample (e.g., not portions of the interior of the housing on either side of the sample). This may desirably block gas or other material within housing 110 from leaking out through measurement port 116. In an exemplary embodiment, measurement port 116 has a diameter of no more than the width of the sample.

In an exemplary embodiment, frame 130 is positioned in order to secure the sample in an approximately central region of the housing 110. As shown in FIG. 1A, frame 130 may be adapted to secure the sample in an approximately axial orientation within the housing (i.e., parallel to an axis of the housing) to enable cross- sectional viewing of the sample through measurement port 116. Nonetheless, while FIGS. 1A and 1C illustrate the sample in a cross-sectional viewing configuration, it will be understood that the invention is not so limited. The frame may be adapted to secure the sample in alternative orientations, as would be understood from one of ordinary skill in the art from the description herein. For example, the frame may be adapted to secure the sample in an approximately radial orientation within the housing (i.e., parallel to the top and bottom surfaces of the housing).

The size and shape of frame 130 may be selected to correspond to the size and shape of housing 110 and the sample to be measured by system 100. As shown in FIG. 1A, frame 130 may be sized to contact only an outer edge of the sample, so that the sample is effectively exposed to the conditions within housing 110.

As shown in FIG. 1A, frame 130 is integrally formed with housing 110. However, the invention is not so limited. Frame 130 may be removably positioned within housing 110, so that multiple different frames 130 may be used with the same housing 110 to accommodate a number of different samples and/or sample positions.

Frame 130 may form at least part of a divider 140 positioned within housing 110. Divider 140 separates housing 110 into multiple distinct zones. Divider 140 may be formed solely by housing 110 and frame 130. Alternatively when the sample is secured by frame 130, the sample may form part of divider 140. Divider 140 substantially prevents passage of gas between the distinct zones.

In an exemplary embodiment, divider 140 separates the interior of housing 110 into a first zone 142a and a second zone 142b, as shown in FIG. 1A. Each zone 142 within housing 110 may desirably have its own gas inlet 112 and its own gas outlet 114, in order to control the operating conditions within housing 110.

In an exemplary embodiment, divider 140 may take a unibody form, as shown in FIG. ID. The unibody divider 140 comprises an interior space within which the sample may be positioned. The unibody divider 140 further comprises a plurality of inlet/outlet ports 144 for delivery gas from gas inlets 112 to the sample and from the sample to gas outlets 114. Inlet/outlet ports 144 may include a pair of concentric lumens for forming a single inlet/outlet in a wall of divider 140. Unibody divider 140 desirably acts as a subchamber within housing 110, in order to isolate gas delivery from the outside directly to the sample surface.

Heater 150 is positioned within housing 110. Heater 150 is operable to heat an interior of housing 110 and/or the sample to be measured to a predetermined temperature. Heater 150 desirably maintains a diameter which allows adequate space under a scanning portion of the measurement device. For example, when the measurement device is an AFM, a suitable diameter may be approximately 1" or less, though with customized leg extenders larger diameter heaters could be accommodated. Heater 150 may desirably be positioned with a small gap between heater 150 and the sample, in order to effectively heat the sample to be measured, as shown in FIG. 1A. In a preferred embodiment, heater 150 may form part of frame 130 and/or be incorporated within frame 130, such that heater 150 directly contacts the sample to be measured when the sample is secured within frame 130. In this embodiment, the heater and the frame may be a single element, which may simplify construction and/or operation of the system .

In a particular preferred embodiment, frame 130 may include a conductive (e.g . copper) slab extending between the sample to be measured and heater 150. The copper slab may be configured to efficiently transfer heat between heater 150 and the sample.

In an exemplary embodiment, heater 150 is an adjustable heating element. The adjustable heating element is configured to enable a user to select the temperature within the interior of housing 110, e.g., using control signals sent via heater connection 120. For example, when a fuel cell is used at the sample to be measured in situ, heater 150 may be adjusted to heat the interior of the housing to a temperature from approximately 400°C to approximately 1000°C, and more preferably, from approximately 500°C to approximately 600°C. Suitable heating elements for use as heater 150 include, for example, a Model 101275 W 0₂ Button Heater, provided by Heatwave Labs, of Watsonville, CA, US. Other suitable heaters 150 will be known to one of ordinary skill in the art from the description herein.

System 100 is not limited to the above described components, but may include alternative or additional components, as would be understood by one of ordinary skill in the art.

For one example, system 100 may include a sample to be measured 170. In an exemplary embod iment, sample 170 com prises a fuel cell . The fuel cell may comprise an electrolyte material 172 positioned between a pair of electrodes 174 (i.e. an anode and a cathode), as shown in FIG, 1C. Suitable fuel cells to be tested by system 100 include, for example, solid oxide fuel cel ls (SOFCs) . Other suitable fuel cells will be known to one of ordinary skill in the art from the description herein .

In this embodiment, a measurement device 180 may be used to measure characteristics of the fuel cell under normal operating conditions of the fuel cell within housing 110. In operation, the fuel cell involves the reduction of oxygen at the cathode into ions which migrate to the anode via the electrolyte where they oxidize a hydrogen- based fuel to form water and release electrons. Suitable measurement devices for use as measurement device 180 include, for example, conventional atomic force

microscopes (AFMs). As set forth above, system 100 is advantageously usable with conventional AFMs and/or other measurement devices, thereby avoiding the expense of specialized or modified measurement devices specifically intended for use at high operating temperatures. Other suitable measurement devices will be known to one of ordinary skill in the art from the description herein.

For another example, system 100 may include one or more gas sources (not shown). In an exemplary embodiment, system 100 includes a source of oxygen coupled to gas inlet 112a, in order to provide gas containing oxygen to the interior of housing 110, and a source of hydrogen coupled to gas inlet 112b, in order to provide gas containing hydrogen to the interior of housing 110. These gases provided on either side of the fuel cell will enable to fuel cell to operate normally within housing 110, so that scanning can be performed under normal operating conditions of the fuel cell. The flow of gas from sources into housing 110 (via gas inlets 112a, 112b) and out of housing 110 (via gas outlets 114a, 114b) may be controlled using conventional gas flow control mechanisms, as would be understood to one of ordinary skill in the art from the description herein.

To measure a reasonably efficient fuel cell, three stimuli are typically necessary: elevated temperatures to ensure higher ion conductivity, electrical bias to assist necessary reactions, and various gases, whether an oxidant like oxygen or a fuel such as hydrogen or methane. These stimuli may be provided by the components of system 100. For example, the elevated temperature may be provided through operation of heater 150; electrical bias may be provided via electrical connections 118a and 118b; and the oxidant and fuel may be provided from the respective gas sources described above.

FIG. 2 illustrates an method 200 for performing in situ measurements in accordance with aspects of the present invention. Method 200 may be used to test fuel cell materials under operating conditions. As a general overview, method 200 includes securing a sample within a housing, heating the interior of the housing, and scanning the sample. Additional details of method 200 are described herein with respect to system 100.

In step 210, a sample is secured within a housing. In an exemplary embodiment, sample 170 is secured within housing 110. As set forth above, housing 110 defines a plurality of gas inlets 112a, 112b, a plurality of gas outlets 114a, 114b, and a measurement port 116. Sample 170 is secured in such a position that it is visible from outside of housing 110 through measurement port 116.

In step 220, the interior of the housing is heated. In an exemplary embodiment, the interior of housing 110 is heated with heater 150. The interior of housing 110 may be heated to a predetermined temperature, which may be adjustable where heater 150 comprises an adjustable heater element. Q

In step 230, the sample is scanned. In an exemplary embodiment, sample 170 is scanned while secured within housing 110 via measurement port 116. Sample 170 may be scanned, for example, with an atomic force microscope.

An exemplary operation of the AFM to measure a fuel cell will now be described in accordance with aspects of the present invention. During operation of the fuel cell within housing 110, the AFM performs two measurements along the surface of the fuel cell's cross-section. In the first pass, the AFM collects a topographic image of the fuel cell surface in non-contact mode. In the second pass, the conductive tip of the AFM is placed under an AC bias using a lock-in amplifier, in order to detect longer range electrostatic forces between the tip and sample. A feedback loop then applies a DC bias in order to compensate the contact potential difference between the tip and sample surface, thereby creating an image of the surface potential of the fuel cell cross-section. This technique is known as scanning surface potential microscopy (SSPM) or Kelvin Probe Force Microscopy (KPFM). In evaluating other energy storage, conversion, and harvesting systems other electrically-based AFM based techniques could potentially be employed, including but not limited to electrostatic force microscopy (EFM), scanning capacitance microscopy (SCM), conductive AFM (cAFM), scanning impedance microscopy (SIM), nanoscale impedance spectroscopy, scanning microwave microscopy (SMM), and electrochemical strain microscopy (ESM), amongst others.

Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.

Claims

What is Claimed :

1. A system for performing in situ measurements of a fuel cell comprising :

a housing defining a plurality of gas inlets, a plurality of gas outlets, and a measurement port;

a frame positioned within the housing, the frame adapted to secure the fuel cell within the housing in such a position that at least one of the plurality of gas inlets and at least one of the plurality of gas outlets are positioned on each side of the fuel cell, the frame positioning the fuel cell such that at least a portion of the fuel cell is accessible via the measurement port; and

a heater positioned within the housing, the heater operable to heat the fuel cell to a predetermined temperature.

2. The system of claim 1, wherein

the housing has an approximately cylindrical shape; and

the measurement port is defined in an axial surface of the housing .

3. The system of claim 2, wherein

the frame is adapted to secure the fuel cell in an approximately axial orientation within the housing .

4. The system of claim 3, wherein

when the fuel cell is secured by the frame, the measurement port has a field of view including a cross-section of the fuel cell .

5. The system of claim 4, wherein

when the fuel cell is secured by the frame, the measurement port has a field of view including only the cross-section of the fuel cell .

6. The system of claim 1, further comprising a d ivider positioned within the interior of the housing, the divider separating the interior of the housing into multiple distinct zones.

7. The system of claim 6, wherein each of the zones comprises at least one of the plurality of gas inlets and one of the plurality of gas outlets.

8. The system of claim 6, wherein

when the fuel cell is secured by the frame, the fuel cell forms part of the divider.

9. The system of claim 1, wherein the heater comprises an adjustable heating element configured to enable a user to select the temperature within the interior of the housing .

10. The system of claim 9, wherein the heater is operable to heat the interior of the housing to a temperature from approximately 400°C to approximately 1000°C.

11. The system of claim 1, wherein the heater forms part of the frame, and the heater directly contacts the fuel cell when the fuel cell is secured by the frame.

12. The system of claim 1, further comprising :

the fuel cell;

a source of oxygen coupled to provide gas containing oxygen to one of the plurality of gas inlets; and

a sou rce of hydrogen coupled to provide gas containing hydrogen to another one of the plurality of gas inlets.

13. A method for performing in situ measurements of a fuel cell comprising :

secu ring the fuel cell to be measured within a housing, the housing defining a plurality of gas inlets, a plurality of gas outlets, and a measurement port such that at least one of the plurality of gas inlets and at least one of the plurality of gas outlets is positioned on each side of the fuel cell and at least a portion of the fuel cell is accessible via the measu rement port;

heating the fuel cell to a predetermined temperature; and scanning the fuel cell through the measurement port.

14. The method of claim 13, wherein the step of scanning the fuel cell comprises scanning the fuel cell through the measurement port with an atomic force microscope.