Patent Publication Number: US-2022231305-A1

Title: Systems and methods for refurbishing fuel cell stack components

Description:
FIELD 
     The present disclosure is directed to systems and methods for refurbishing fuel cell stack components in general, and to using a laser to remove seal and ceramic barrier material from fuel cell interconnects. 
     BACKGROUND 
     A typical solid oxide fuel cell (SOFC) stack includes multiple SOFCs separated by interconnects (ICs) which provide both electrical connection between adjacent cells in the stack and channels for delivery and removal of fuel and oxidant. When hydrocarbons are used for fuel, some of the hydrocarbons may catalytically decompose or crack on the surface of the interconnect, leaving a deposit of coke. These coke deposits can clog the channels adversely affecting the performance of the fuel cell stack. 
     The fuel cell stack may be reconditioned by refurbishing the ICs. A typical IC refurbishment process may include the following steps: (1) singulation (separating interconnects and individual fuel cells in a stack from one another), (2) removal of electrolyte debris from the interconnects, (3) removal of any other remaining internal stack components (if any) from the interconnects and (4) removal of seals and protective coatings. 
     Prior singulation methods include mechanically prying the stack apart using a hand held tool. This process is time-consuming and prone to damaging the interconnects, by chipping, cracking, or inducing camber (curvature). 
     After singulation, most of the electrolyte can be scraped off, but material left around the seal region is typically very well adhered to the IC and hard to remove. The last step to achieving a clean part is typically removing the metal oxide (e.g., chromium oxide) that grows on the fuel side of the chromium alloy interconnects and residual seal material. A grit blasting process typically used in removing these oxides is costly, time consuming, difficult to control, and can cause damage to the part by inducing camber and excessive erosion of the part. 
     SUMMARY 
     According to various embodiments a method of refurbishing a singulated fuel cell stack interconnect includes scanning a pulsed laser beam on an air side of the interconnect to vaporize seal and corrosion barrier layer residue without vaporizing a metal oxide layer located on the air side of the interconnect below the corrosion barrier layer residue, and scanning a second pulsed laser beam which is different from the first pulsed laser beam on the exposed metal oxide layer on the air side of the interconnect to reflow the metal oxide layer without removing the metal oxide layer. 
     According to various embodiments, a method of coating a fuel cell stack interconnect comprising fuel holes extending through the interconnect, air channels located on the air side of the interconnect, ring seal regions surrounding the fuel holes located on the air side of the interconnect, and a metal oxide layer located on the air side of the interconnect, the method comprising forming microcavities through the metal oxide layer in the seal ring regions by laser drilling, depositing a corrosion barrier layer on the metal oxide layer and into the microcavities at least on the seal ring regions; and depositing a seal material on the corrosion barrier layer in the seal ring regions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of a SOFC stack, according to various embodiments of the present disclosure. 
         FIG. 1B  is a cross-sectional view of a portion of the stack of  FIG. 1A . 
         FIG. 2A  is a plan view of an air side of an interconnect, according to various embodiments of the present disclosure. 
         FIG. 2B  is a plan view of a fuel side of the interconnect of  FIG. 2A . 
         FIG. 3A  is a plan view of an air side of a fuel cell, according to various embodiments of the present disclosure. 
         FIG. 3B  is a plan view of a fuel side of the fuel cell of  FIG. 3A . 
         FIG. 4  is a cross-sectional view of a fuel cell stack including interconnects that include a metal oxide coating and a corrosion barrier layer, according to various embodiments of the present disclosure. 
         FIG. 5  is a process flow diagram illustrating a method of refurbishing fuel cell interconnects, according to various embodiments of the present disclosure. 
         FIG. 6A-6B  are plan views showing laser irradiation patterns that may be applied to the respective air and fuel sides of an interconnect, during the refurbishing method of  FIG. 5 . 
         FIG. 6C  is a plan view showing the air side of an interconnect after resurfacing according to the method of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     The various embodiments will be described in detail with reference to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. References made to particular examples and implementations are for illustrative purposes, and are not intended to limit the scope of the invention or the claims. 
     It will be understood that when an element or layer is referred to as being “on” or “connected to” another element or layer, it can be directly on or directly connected to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on” or “directly connected to” another element or layer, there are no intervening elements or layers present. It will be understood that for the purposes of this disclosure, “at least one of X, Y, and Z” can be construed as X only, Y only, Z only, or any combination of two or more items X, Y, and Z (e.g., XYZ, XYY, YZ, ZZ). 
     Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention. It will also be understood that the term “about” may refer to a minor measurement errors of, for example, 5 to 10%. In addition, weight percentages (wt %) and atomic percentages (at %) as used herein respectively refer to a total weight or number of atoms of a corresponding composition. 
     Words such as “thereafter,” “then,” “next,” etc. are not necessarily intended to limit the order of the steps; these words may be used to guide the reader through the description of the methods. Further, any reference to claim elements in the singular, for example, using the articles “a,” “an” or “the” is not to be construed as limiting the element to the singular. 
     The term “fuel cell stack,” as used herein, means a plurality of stacked fuel cells that can optionally share a common fuel inlet and exhaust passages or risers. The “fuel cell stack,” as used herein, includes a distinct electrical entity which contains two end plates which are connected directly to power conditioning equipment and the power (i.e., electricity) output of the stack or comprises a portion of a fuel cell column that contains terminal plates which provide electrical output. 
     Various embodiments include methods for refurbishing components, such as interconnects (ICs), of a fuel cell stack, such as a solid oxide fuel cell (SOFC) stack. Embodiments include methods of singulating, electrolyte removal, seal and ceramic barrier removal, and interconnect coating rejuvenation. The various methods of singulating, electrolyte removal, seal and ceramic barrier removal and interconnect coating rejuvenation may be used either singly or in combination or in combination with conventional techniques. 
       FIG. 1A  is a perspective view of a fuel cell stack  100 , and  FIG. 1B  is a sectional view of a portion of the stack  100 , according to various embodiments of the present disclosure. Referring to  FIGS. 1A and 1B , the stack  100  may be a solid oxide fuel cell (SOFC) stack that includes fuel cells  1  separated by interconnects  10 . Referring to  FIG. 1B , each fuel cell  1  comprises a cathode  3 , a solid oxide electrolyte  5 , and an anode  7 . 
     Various materials may be used for the cathode  3 , electrolyte  5 , and anode  7 . For example, the anode  7  may comprise a cermet layer comprising a metal-containing phase and a ceramic phase. The metal-containing phase may include a metal catalyst, such as nickel (Ni), cobalt (Co), copper (Cu), alloys thereof, or the like, which operates as an electron conductor. The metal catalyst may be in a metallic state or may be in an oxide state. For example, the metal catalyst forms a metal oxide when it is in an oxidized state. Thus, the anode  7  may be annealed in a reducing atmosphere prior to operation of the fuel cell  1 , to reduce the metal catalyst to a metallic state. 
     The metal-containing phase may include nickel in a reduced state. This nickel-containing phase may form nickel oxide when it is in an oxidized state. Thus, the anode  7  is preferably annealed in a reducing atmosphere prior to operation to reduce the nickel oxide to nickel. 
     According to some embodiments, the metallic phase may include the metal catalyst and a dopant. For example, the metallic phase may be represented by Formula 1: [D x M 1-x ] y O. In Formula 1, D is a dopant (in any oxidation state) selected from magnesium (Mg), calcium (Ca), titanium (Ti), aluminum (Al), manganese (Mn), tungsten (W), niobium (Nb), chromium (Cr), iron (Fe), vanadium (V), praseodymium (Pr), cerium (Ce), zirconium (Zr) or the like, or any combination thereof. In some embodiments, D may be Ca, Mg, and/or Ti. M is a metal catalyst selected from nickel (Ni), cobalt (Co), copper (Cu), or alloys thereof. X may range from about 0.01 to about 0.1, and y may range from about 1 to about 2. In other embodiments, x may range from about 0.01 to about 0.04. For example, x may be about 0.02 and y may be either 1 or 2. 
     Accordingly, the metallic phase may comprise from about 1 to about 10 atomic percent (“at %”) of the metal oxide dopant and about 99 to about 90 at % of the metal catalyst. For example, the metallic phase may comprise from about 2 to about 4 at % of the metal oxide dopant and about 98 to about 96 at % of the metal catalyst, as manufactured before being reduced. 
     The ceramic phase of the anode  7  may include, but is not limited to gadolinia-doped ceria (GDC), samaria-doped ceria (SDC), ytterbia-doped ceria (YDC), scandia-stabilized zirconia (SSZ), ytterbia-ceria-scandia-stabilized zirconia (YCSSZ), or the like. In the YCSSZ, scandia may be present in an amount equal to 9 to 11 mol %, such as 10 mol %, ceria may present in amount greater than 0 (e.g., at least 0.5 mol %) and equal to or less than 2.5 mol %, such as 1 mol %, and at least one of yttria and ytterbia may be present in an amount greater than 0 and equal to or less than 2.5 mol %, such as 1 mol %, as disclosed in U.S. Pat. No. 8,580,456, which is incorporated herein, by reference. Yttria stabilized zirconia (YSZ) may be excluded from the ceramic phase of the anode  7 . 
     The electrolyte  5  may comprise a stabilized zirconia, such as scandia-stabilized zirconia (SSZ), yttira-stabilized zirconia (YSZ), scandia-ceria-stabilized zirconia (SCSZ), scandia-ceria-yttira-stabilized zirconia (SCYSZ), or the like. Alternatively, the electrolyte  5  may comprise another ionically conductive material, such as a samaria-doped ceria (SDC), gadolinium-doped ceria (GDC), or yttria-doped ceria (YDC). 
     The cathode  3  may comprise a layer of an electrically conductive material, such as an electrically conductive perovskite material, such as lanthanum strontium manganite (LSM). Other conductive perovskites, such as lanthanum strontium cobaltite (LSC), lanthanum strontium cobalt manganite (LSCM), lanthanum strontium cobalt ferrite (LSCF), lanthanum strontium ferrite (LSF). La 0.85 Sr 0.15 Cr 0.9 Ni 0.1 O 3  (LSCN), etc., or metals, such as Pt, may also be used. The cathode  3  may also contain a ceramic phase similar to the anode  7 . The electrodes and the electrolyte may each comprise one or more sublayers of one or more of the above described materials. 
     Furthermore, if desired, additional contact or current collector layers may be placed over the cathode  3  and anode  7 , while additional interfacial layers, such as doped ceria interfacial layers, may be located between the electrodes  3 ,  7  and the electrolyte  5 . For example, a Ni or nickel oxide anode contact layer and an LSM or LSCo cathode contact layer may be formed on the anode  7  and cathode  3  electrodes, respectively. 
     Fuel cell stacks are frequently built from a multiplicity of fuel cells  1  in the form of planar elements, tubes, or other geometries. Although the fuel cell stack  100  in  FIG. 1A  is vertically oriented, fuel cell stacks may be oriented horizontally or in any other direction. Fuel and air may be provided to the electrochemically active surface, which can be large. For example, fuel may be provided through fuel holes  22  (e.g., fuel riser openings) formed in each interconnect  10  and fuel cell  1 , while air may be provided from the side of the stack between air side ribs of the interconnects  10 . 
     Each interconnect  10  electrically connects adjacent fuel cells  1  in the stack  100 . In particular, an interconnect  10  may electrically connect the anode  7  of one fuel cell  1  to the cathode  3  of an adjacent fuel cell  1 .  FIG. 1B  shows that the lower fuel cell  1  is located between two interconnects  10 . A Ni mesh (not shown) may be used to electrically connect the interconnect  10  to the anode  7  of an adjacent fuel cell  1 . 
     Each interconnect  10  includes fuel-side ribs  12 A that at least partially define fuel channels  8 A and air-side ribs  12 B that at least partially define oxidant (e.g., air) channels  8 B. The interconnect  10  may operate as a gas-fuel separator that separates a fuel, such as a hydrocarbon fuel, flowing to the fuel electrode (i.e. anode  7 ) of one cell in the stack from oxidant, such as air, flowing to the air electrode (i.e. cathode  3 ) of an adjacent cell in the stack. At either end of the stack  100 , there may be an air end plate or fuel end plate (not shown) for providing air or fuel, respectively, to the end electrode. 
     Each interconnect  10  may be made of or may contain electrically conductive material, such as a metal alloy (e.g., chromium-iron alloy) which has a similar coefficient of thermal expansion to that of the solid oxide electrolyte in the cells (e.g., a difference of 0-10%). For example, the interconnects  10  may comprise a metal (e.g., a chromium-iron alloy, such as 4-6 weight percent iron, optionally 1 wt % or less yttrium and balance chromium alloy), and may electrically connect the anode or fuel-side of one fuel cell  1  to the cathode or air-side of an adjacent fuel cell  1 . An electrically conductive contact layer, such as a nickel contact layer, may be provided between anodes  7  and each interconnect  10 . Another optional electrically conductive contact layer may be provided between the cathodes  3  and each interconnect  10 . 
       FIG. 2A  is a top view of the air side of the interconnect  10 , and  FIG. 2B  is a top view of a fuel side of the interconnect  10 , according to various embodiments of the present disclosure. Referring to  FIGS. 1B and 2A , the air side includes the air channels  8 B that extend from opposing first and second edges of the interconnect  10 . Air flows through the air channels  8 B to a cathode  3  of an adjacent fuel cell  1 . 
     The interconnect  10  may include ring seal regions  20 R that surround the fuel holes  22 . Ring seals  20  may be disposed in the ring seal regions  20 R, surrounding the fuel holes  22 , to prevent fuel from contacting the air side of the interconnect  10 . The air side of the interconnect  10  may include strip seal regions  24 R disposed on opposing edges of the interconnect  10 . Elongated rectangular seals  24  (e.g., strip seals) may be disposed on the strip seal regions  24 R. The ring and strip seals  20 ,  24  may be formed of a glass or glass-ceramic material. The ring seal regions  22 R and the strip seal regions  24 R may be planar elevated regions that do not include ribs or channels. The surfaces of the ring seal regions  22 R and the strip seal regions  24 R may be coplanar with tops of the ribs  12 B. 
     Referring to  FIGS. 1B and 2B , the fuel side of the interconnect  10  may include a fuel flow region  30 R including the fuel channels  8 A and fuel manifolds  28 . Fuel flows from one of the fuel holes  22  (e.g., inlet fuel hole that forms part of the fuel inlet riser), into the adjacent manifold  28 , through the fuel channels  8 A, and to an anode  7  of an adjacent fuel cell  1 . Excess fuel may flow into the other fuel manifold  28  and then into the other fuel hole  22 . A frame seal  26  is disposed on a frame seal region  26 R of the fuel side of the interconnect  10 . The frame seal region  26 R may be an elevated plateau which does not include ribs or channels. The surface of the frame seal region  26 R may be coplanar with tops of the ribs  12 A. 
       FIG. 3A  is a plan view of a cathode side (e.g., air side) of the fuel cell  1 , and  FIG. 3B  is a plan view of an anode side (e.g., fuel side) of the fuel cell  1 , according to various embodiments of the present disclosure. Referring to  FIGS. 1A, 1B, 3A, and 3B , the fuel cell  1  may include fuel holes  22 , the electrolyte  5 , the cathode  3  and the anode  7 . The cathode  3  may be disposed on a first side of the electrolyte  5 . The anode  7  may be disposed on an opposing second side of the electrolyte  5 . 
     The fuel holes  22  may extend through the electrolyte  5  and may be arranged to overlap with the fuel holes  22  of the interconnects  10 , when assembled in the fuel cell stack  100 . The cathode  3  may be printed on the electrolyte  5  so as not to overlap with the ring seals  20  and the strip seals  24  when assembled in the fuel cell stack  100 . The anode  7  may have a similar shape as the cathode  3 . The anode  7  may be disposed so as not to overlap with the frame seal  26 , when assembled in the stack  100 . In other words, the cathode  3  and the anode  7  may be recessed from the edges of the electrolyte  5 , such that corresponding edge regions of the electrolyte  5  may directly contact the corresponding seals  20 ,  24 ,  26 . 
       FIG. 4  is a cross-sectional view of a fuel cell  1  and adjacent interconnects  10  of a fuel cell stack  100 , according to various embodiments of the present disclosure. The features of the lower interconnect  10  of  FIG. 4  are shown in detail. However, both interconnects  10  may have the same features. A metal oxide coating or layer  32  may be disposed on the air sides of the interconnects  10 , and a corrosion barrier layer  34  may be disposed on the metal oxide layer  32 . The metal oxide layer  32  may be formed of, for example, lanthanum strontium manganite (“LSM”) and/or manganese cobalt oxide (“MCO”) spinel coating materials and may be disposed on the air side ribs  12 B and/or in the air channels  8 B of the interconnects  10 . 
     The corrosion barrier layer  34  may be disposed on the metal oxide layer  32  at least below the ring seals  20 . In some embodiments, the corrosion barrier layer  34  may optionally also be disposed below the strip seals  24 , or may cover the entire metal oxide layer  32 . The corrosion barrier layer  34  may operate as a barrier to diffusion of at least one of manganese or cobalt from a metal oxide layer  32  into the ring seals  20 . Specifically, the corrosion barrier layer  34  preferably lacks any Mn and/or Co (or at least contains less than 5 at % of Mn and/or Co) and prevents Mn and/or Co diffusion from the metal oxide layer into the ring seals  20 , in order to prevent the Mn and/or Co diffusion from the ring seals  20  to the adjacent electrolyte  5 . 
     The corrosion barrier layer  34  may comprise a glass ceramic material described in U.S. Pat. No. 9,583,771 B2, issued Feb. 28, 2017 and incorporated herein by reference in its entirety. The corrosion barrier layer  34  may comprise a glass ceramic layer formed from a substantially glass barrier precursor layer containing at least 90 wt. % glass (e.g., 90-100 wt. % glass, such as around 99 to 100 wt. % amorphous glass and 0 to 1 wt. % crystalline phase) applied to a surface of interconnects in the SOFC stack. In one embodiment, the glass barrier precursor layer contains at least 90 wt. % glass and comprises: 
     45-55 wt. % silica (SiO 2 ); 
     5-10 wt. % potassium oxide (K 2 O); 
     2-5 wt. % calcium oxide (CaO); 
     2-5 wt. % barium oxide (BaO); 
     0-1 wt. % boron trioxide (B 2 O 3 ); 
     15-25 wt. % alumina (Al 2 O 3 ); and 
     20-30 wt. % zirconia (ZrO 2 ) on an oxide weight basis. 
     In one preferred embodiment, a glass barrier precursor layer comprises: 
     44.6 wt. % silica; 
     6.3 wt. % potassium oxide; 
     2.4 wt. % calcium oxide; 
     2.4 wt. % barium oxide; 
     19.1 wt. % alumina; 
     0.1 wt. % boron trioxide; and 
     25.1 wt. % zirconia on an oxide weight basis. 
     In some embodiments, a chromium oxide layer  36  may be formed on the fuel side of the interconnect  10 . In particular, chromium of the chromium-iron alloy interconnect  10  material may form a chromium oxide layer  36  that accumulates on the fuel side of the interconnect  10 . 
     Fuel Cell Component Refurbishing 
     According to various embodiments of the present disclosure, systems and methods of refurbishing fuel cell stack components are provided. For example, at the end of the operating life of a fuel cell stack, the stack may be disassembled and components thereof may be recycled (i.e., reused in a new fuel cell stack) after being refurbished. 
       FIG. 6  is a process flow diagram illustrating a method of recycling fuel cell interconnects, according to various embodiments of the present disclosure. Referring to  FIGS. 1A, 4 and 5 , in step  602 , the fuel cell stack  100  may be may be removed from a fuel cell system and singulated to separate the interconnects  10  from one another. 
     Any suitable method of singulation may be used. For example, a stack may be singulated mechanically, hydraulically, or thermally, and fuel cell components may be removed therefrom, as disclosed in U.S. Pat. No. 8,535,841, issued on Sep. 17, 2013, and U.S. Pat. No. 10,756,355 B2, issued on Aug. 25, 2020, which are incorporated herein by reference in their entireties. 
     In step  604 , stack component debris may be removed from each interconnect  10 . For example, fuel cell electrolyte, seals, inks, and/or conductive layers, such as nickel mesh layers, which remain attached to the interconnect  10 , may be removed. For example, a wire brush or compressed air may be used to remove such debris. In some embodiments, a fuel cell electrolyte may be cracked using a die in order to facilitate fuel cell component debris removal. 
     After removal of the debris, stack component residues may remain on the interconnect  10 . For example, the residues may include glass, ceramic, and/or glass/ceramic material residues, such as residues from ceramic electrolyte, glass seals, and/or ceramic barrier layers, or the like, may remain on the interconnect  10 . In particular, the residues may include the seal  20  and/or  24  residue, corrosion barrier layer  34  disposed on the ring seal regions  20 R on the fuel side of the interconnect  10 , and the chromium oxide layer  36  disposed on the fuel side of the interconnect  10 . 
     In step  606  the air side and the fuel side of the interconnect  10  may be laser-irradiated to remove the residues. The air and fuel sides of the interconnect  10  may be laser irradiated in any order, or simultaneously. In particular, step  606  may include scanning at least portions of the fuel and air sides of the interconnect  10  with one or more pulsed laser beams, in order to heat the residues to a temperature sufficient to vaporize and/or dislodge the residues. 
     It has been determined that precise control of the irradiation of the interconnect  10  may allow for the removal of the residues without damaging the relatively expensive metal oxide layer  32  on the air side of the interconnect  10 . For example, excessive localized heating of the interconnect  10  may result in the formation of cracks and/or may damage the metal oxide layer  32  on the interconnect. Accordingly, characteristics of the laser beam may be controlled, such as the power, pulse frequency, scan speed and/or beam spot diameter, such that the residues may be vaporized without the damaging the metal oxide layer  32  and/or the interconnect  10 . 
     According to some embodiments, a single laser beam may be used to irradiate one or both of the fuel and air sides of the interconnect  10 . In other embodiments, one or more laser beams, which may be generated by one or more laser sources, may be used to irradiate each side of the interconnect  10 . Each laser beam may be controlled with a scanner configured to control scanning of the laser beam across the interconnect  10 . For example, laser beams may be selectively scanned in a raster pattern, a vector pattern, a serpentine pattern, or the like, in order to heat the surface of the interconnect  10  to a temperature sufficient to vaporize the residues. Alternatively, the interconnect  10  may be moved in a support stage relative to the laser beam to scan the beam across the interconnect. 
     Accordingly, the residues may be removed from the interconnect  10  in a rapid manner Laser line speeds may exceed 24 inches per second (e.g., 25 to 500 inches per second) in some embodiments. Laser exposure times for the residues may be less than 1 sec (e.g., 0.05 to 0.9 sec). However, the present disclosure is not limited to any particular type of laser, travelling time, or exposure time. The laser beam may be configured vaporize and/or delaminate the fuel cell debris from the interconnect  10 . For example, the laser may vaporize seals bonding other fuel cell debris to the interconnect  10 , resulting in the removal of such materials. 
     In some embodiments, the laser beam(s) may be generated by a laser source, such as a pulsed infrared fiber laser source configured to generate a laser beam having a wavelength greater than 800 nm and less than 5,000 nm, such as wavelength ranging from about 1060 nm to about 1075 nm, such as from about 1062 nm to about 1066 nm, or about 1064 nm. A fiber laser includes a rare earth element doped optical fiber active gain medium. The rare earther elements may include erbium, ytterbium, neodymium, dysprosium, praseodymium, thulium and/or holmium. The laser source may have a peak power output ranging from 100 W to 3000 W, such as from 500 W to 1000 W. The laser source may generate a laser beam spot having a beam spot size (e.g., diameter) of 1.5 mm or less, such as 1 mm or less, such as about 0.5 mm to about 1 mm, such as about 0.6 mm to 0.8 mm. The present inventors determined that using a pulsed laser beam with the relatively small beam spot size (e.g., 1.5 mm or less) rather than a continuous laser beam with a relatively large beam spot size (e.g. 2 mm or greater) results in a higher peak power for a shorter duration, which is capable of removing the residue without vaporizing the metal oxide layer  32  or damaging the interconnect  10 . Thus, the refurbished interconnect  10  does not have to be recoated with a relatively expensive metal oxide layer  32 . 
       FIG. 6A  illustrates laser a laser irradiation pattern that may be applied to the air side of a singulated interconnect  10 , and  FIG. 6B  illustrates laser irradiation pattern that may be applied to the fuel side of the interconnect  10 , according to various embodiments of the present disclosure.  FIG. 6C  is a top view of the air side of the interconnect  10 , after resurfacing, according to various embodiments of the present disclosure. 
     Referring to  FIGS. 5 and 6A , in step  606 , the method may include scanning one or more a laser beams across the strip seal regions  24 R and the ring seal regions  20 R of the air side of the interconnect  10 , using one or more scanning passes by moving the laser beam and the interconnect relative to each other. Either the laser beam and/or the interconnect  10  may be moved to generate a scan of the laser beam across the interconnect  10 . 
     For example, step  606  may include performing a first scanning pass, during which the strip seal regions may be scanned with a first laser beam. The first laser beam may be a pulsed laser beam having a peak power ranging from about 800 W to about 1250 W, such as from about 900 W to about 1100 W, from about 950 W to about 1050 W, or about 1000 W. The first laser beam may have a pulse frequency ranging from about 5 kHz to about 15 kHz, such as from about 8 kHz to about 13 kHz, or about 10 kHz to 11 kHz. The first laser beam may have a scanning speed ranging from about 2500 mm/s to about 3500 mm/s, such as from about 2750 mm/s to about 3250 mm/s, or about 3000 mm/s. The first laser beam may have a beam spot size (e.g., diameter) of 1.5 mm or less, such as 1 mm or less, such as about 0.5 mm to about 1 mm, such as about 0.6 mm to 0.8 mm. The first laser beam may have a pulse width ranging from about 50 ns to about 150 ns, such as from about 75 ns to about 125 ns, or about 100 ns. The frequency and/or dwell time may be changed during the first scanning pass to sequentially remove different residues (e.g., to remove seal reside followed by removing the corrosion barrier layer residue). 
     Step  606  may include performing a second scanning pass, during which the strip seal regions  24 R may be scanned for a second time with a second laser beam. The second laser beam may be a pulsed laser beam different from the first laser beam using during the first scanning pass. The second laser beam may have at least one of a lower peak power, a shorter pulse width, a faster scanning speed, a smaller beam spot size, and/or a higher pulse frequency than the first laser beam used during the first scanning pass. The smaller beam spot size of the second laser beam results in a higher power density than that of the first laser beam. The second laser beam may have a peak power ranging from about 250 W to about 750 W, such as from about 400 W to about 600 W, from about 450 W to about 550 W, or about 500 W. The second laser beam may have a pulse frequency ranging from about 20 kHz to about 40 kHz, such as from about 25 kHz to about 35 kHz, or about 30 kHz. The second laser beam may have a scanning speed ranging from about 4500 mm/s to about 5500 mm/s, such as from about 4750 mm/s to about 5250 mm/s, or about 5000 mm/s. The second laser beam may have a beam spot size (e.g., diameter) of less than 0.5 mm, such as a beam spot size ranging from about 0.05 mm to about 0.15 mm, such as from about 0.075 mm to about 0.125 mm, or about 0.1 mm. The second laser beam may have a pulse width ranging from about 15 ns to about 35 ns, such as from about 20 ns to about 30 ns, or about 25 ns. The second laser beam may reflow the metal oxide layer  32  in the strip seal regions  24 R without removing (e.g., vaporizing) the metal oxide layer  32 . Therefore, the metal oxide layer may be smoother and denser (e.g., with rough spots removed and/or pores filled) than after the first scanning pass. 
     Step  606  may include performing a third scanning pass, during which the ring seal regions  20 R are scanned for the first time using a third laser beam. The third laser beam may have similar characteristics to the first laser beam. 
     Step  606  may include performing a fourth scanning pass, during which the ring seal regions  20 R are scanned for a second time using a fourth laser beam. The fourth laser beam may have the similar characteristics to the second laser beam. The fourth laser beam may reflow the metal oxide layer  32  in the ring seal regions  20 R without vaporizing the metal oxide layer  32 . Therefore, the metal oxide layer may be smoother and denser (e.g., with rough spots removed and/or pores filled) than after the third scanning pass. 
     However, in some embodiments, the ring seal regions  20 R may be scanned before, or at the same time as, the strip seal regions  24 R are scanned. As such, the present disclosure is not limited to any particular scanning sequence. Thus, in some embodiments, step  606  may be modified such that the ring seal regions  20 R and the strip seal regions  24 R may be scanned using only two scanning passes. For example, step  606  may be modified such that the ring seal regions  20 R and the strip seal regions  24 R are both scanned during the first scanning pass, using the first laser beam, and then scanned against during the second scanning path using the second laser beam. 
     Referring to  FIGS. 5 and 6B , step  606  may include performing a fifth scanning pass, during which the frame seal region  26 R of the fuel side of the interconnect  10  is scanned using a fifth laser beam. The fifth laser beam may have substantially the same characteristics as the first laser beam. 
     Step  606  may include performing a sixth scanning pass, during which the frame seal region  26 R may be scanned for a second time using a sixth laser beam. The sixth laser beam may have a lower power and/or a faster scanning speed than the fifth laser beam. The sixth laser beam may be a pulsed laser beam having a peak power ranging from about 250 W to about 750 W, such as from about 400 W to about 600 W, from about 450 W to about 550 W, or about 500 W. The sixth laser beam may have a pulse frequency ranging from 5 kHz to about 15 kHz, such as from about 8 kHz to about 13 kHz, or about 10 kHz to 11 kHz. The sixth laser beam may have a scanning speed ranging from about 4500 mm/s to about 5500 mm/s, such as from about 4750 mm/s to about 5250 mm/s, or about 5000 mm/s. The sixth laser beam may have a beam spot diameter ranging from about 0.15 mm to about 0.35 mm, such as from about 0.20 mm to about 0.30 mm, or about 0.25 mm. The sixth laser beam may have a pulse width ranging from about 50 ns to about 150 ns, such as from about 75 ns to about 125 ns, or about 100 ns. 
     Referring to  FIGS. 4, 5, and 6C , in step  608 , the method may include removing the chromium oxide layer  36  from the fuel side of the interconnect  10 . In particular, step  608  may include performing a seventh scanning pass, during which a seventh laser beam may be scanned across all, or substantially all, of the fuel side of the interconnect  10 , in one or more passes, in order to vaporize the chromium oxide layer  36 . The characteristics of the seventh laser beam may be set such that the chromium oxide layer  36  is removed without damaging the underlying fuel side of the interconnect  10 . 
     The seventh laser beam may have at least one of a lower power, a higher frequency, a faster scanning speed and/or a shorter pulse width than the sixth laser beam. For example, the seventh laser beam may be a pulsed laser beam having a peak power ranging from about 200 W to about 600 W, such as from about 300 W to about 500 W, from about 350 W to about 450 W, or about 400 W. The seventh laser beam may have a pulse frequency ranging from about 20 kHz to about 40 kHz, such as from about 25 kHz to about 35 kHz, or about 30 kHz. The seventh laser beam may have a scanning speed ranging from about 7500 mm/s to about 8500 mm/s, such as from about 7750 mm/s to about 8250 mm/s, or about 8000 mm/s. The seventh laser beam may have a beam spot diameter ranging from about 0.6 mm to about 1.0 mm, such as from about 0.7 mm to about 0.9 mm, or about 0.8 mm. The seventh laser beam may have a pulse width ranging from about 15 ns to about 35 ns, such as from about 20 ns to about 30 ns, or about 25 ns. 
     Referring again to  FIGS. 4 and 5 , in step  610 , the method may include reconditioning the air side of the interconnect  10 . In particular, step  610  may include scanning an eighth laser beam across all or substantially all of the air side of the interconnect  10 , during an eight scanning pass, in order to recondition the metal oxide layer  32 . The eighth laser beam may have substantially the same characteristics as the first laser beam. 
     The characteristics of the eighth laser beam may be set such that the metal oxide layer  32  may be partially melted to smooth and densify the surface of the metal oxide layer  32  and/or to remove contaminants therefrom. In particular, the metal oxide layer  32  may be heated to a temperature sufficient to at least partially liquefy the surface of metal oxide layer  32 , resulting in the reflow of the liquefied metal oxide into pores of the remaining metal oxide layer  32 . The process may increase the density of the metal oxide layer  32  and may remove any relatively rough surface regions of the metal oxide layer  32 . 
     The scanning patterns may include horizontal scan lines as shown in  FIG. 6A . However, the present disclosure is not limited to any particular scanning pattern or scan line orientation. For example, the scanning patterns may include vertical scan lines, non-vertical scan lines, horizontal scan lines, serpentine scan lines, or any combination thereof. 
     Referring to  FIGS. 5 and 6C , in step  612 , the method may include resurfacing the ring seal regions  20 R of the air side of the interconnect  10 . In particular, the surface area of the metal oxide layer  32  in the ring seal regions  20 R may be increased by roughening or drilling, in order to increase adhesion between the metal oxide layer  32  and a subsequently deposited barrier layer. 
     In particular, step  612  may include laser drilling the ring seal regions  20 R to form micro cavities  80  in the metal oxide layer  32  or both the metal oxide layer  32  and the interconnect  10 . The microcavities  80  may have a diameter of about 25 μm to about 200 μm, such as from about 50 μm to about 100 μm, or about 75 μm. At least one thousand (e.g., 1,000 to 10,000, such as 5,000 to 6,000) micro cavities  80  may be formed in each ring seal region  20 R. The same pulsed laser beam as the fourth laser beam may be used for laser drilling except that the beam spot size is reduced to 200 microns or less, such as a diameter of 25 μm to about 200 μm, such as from about 50 μm to about 100 μm, or about 75 μm. 
     In some embodiments, step  612  may include depositing a corrosion barrier layer  34 , as shown in  FIG. 4 , on the ring seal regions  20 R, after resurfacing the ring seal regions  20 R. The microcavities  80  improve the adhesion of the corrosion barrier layer  34  to the metal oxide layer  32 . 
     The refurbishing process may leave no visible trace of fuel cell debris. In addition, the interconnect remains free of cracks and/or other damage due that may occur due to excessive heating during a recycling process. In addition, the chromium oxide layer  36  can be removed from the fuel side, and the corrosion barrier layer  34  can be removed from the air side of the interconnect  10  without removing the relatively expensive metal oxide layer  32 . 
     Although the foregoing refers to particular preferred embodiments, it will be understood that the invention is not so limited. It will occur to those of ordinary skill in the art that various modifications may be made to the disclosed embodiments and that such modifications are intended to be within the scope of the invention. All of the publications, patent applications and patents cited herein are incorporated herein by reference in their entirety.