Tech Talk - Chemical Etching for Bipolar Plates - Fuel Cell Technology Explained - Hyfindr Montoya
Hello my name is Steven. Welcome to Hyfindr Tech Talks, where we aim to understand the technology that makes the hydrogen economy work. Today we are going to be looking at bipolar plates again chemically etched bipolar plates. And for this topic we've reached out to a company that has a 50-year history in this area, it's called Elcon Precision. They've worked in several areas with this and are now providing this for the hydrogen economy as well. And from Elcon Precision I am
very pleased to welcome a lady, who's a process engineer there, who's driving this forward and helping to make it more efficient for fuel cell applications, electrolyzer applications or wherever these things may be used. So I'm very particularly pleased to welcome Aurelia Montoya. Welcome to Hyfindr Tech Talks Aurelia. Hi Steven, thank you for having me. Yes and in fact I do need to mention, that you are joining us today via
Zoom, because you're based in California and we'll be talking in this way. So thank you for taking the time and let's go right into it. Aurelia, what are chemically etched bipolar plates? So as I'm sure you know, bipolar plates are chemically conductive or electrically conductive plates, that are used in the fuel cell stacks. So when they're chemically etched the channels and any other features that are critical to the application are chemically etched. And just for understanding, when you mean chemically etched, what is etching? Etching is a subtractive manufacturing process, in which corrosive chemicals attack and dissolve unprotected material, that's left unprotected by photosensitive film.
I'll go into all of that as we move forward. Okay good, unprotected aggressive chemicals, well let's see how that goes. Then please take us deeper help us understand what the process of chemical etching for bipolar plates is. Yeah, so the chemical etching process for bipolar plates can be broken up into eight general steps and so you can see those on the screen there. I'll be going over each of these individually as we move forward, so unless you have any questions about this slide I can move forward to the first one.
So the first step is material selection. Material selection is how we start the process for bipolar plate etching. The material selected for bipolar plates in particular needs to be electrically conductive and low gas permeability, but you also have to make sure the material that's used is etchable. So the metals you see listed here, like copper and its alloys kovar, molybdenum,
hafnium and tungsten are all etchable, but the only ones that are typically used for bipolar plates are aluminum, titanium and stainless steel. And I do have an example of a stainless steel sheet here to show you, so this sheet is stainless steel. It's roughly 0.6mm thick and this can be used to make a bipolar plate. So this will kind of give you an idea of what we start with and what's moving through the process. So on the slide I see all those metals, is this correct? Yes. Okay all right
So moving on to the next step is cleaning. So cleaning is a really important process because it helps prepare the metal surface for lamination, which I'll talk about after this. In the video here you can see the operator is going to dip that metal sheet into a tank, so it gets dipped into tanks of degreasing solutions and mild acidic solutions, that help take off any oils and any contaminants on the surface of the metal. That will allow the film that I'm going to talk about after this adhere, so that we can print the image that we need to and continue with the etching process. So there it's getting rinsed with water and it'll get dried and then ready for the next step. The step after cleaning is lamination. With lamination you can see here in
this small diagram, that with your metal sheet you have two layers on either side, so it's sandwiched between that protective photosensitive film that I mentioned earlier, so we'll see how that gets laminated onto the sheet. In the video here you can see that the operator is feeding that metal sheet that's already gone through cleaning, through two rubber rollers and it's getting coated or laminated with that photosensitive film. Those rollers are applying pressure and they have a temperature of I believe at least 120°C, so that it can properly adhere to that surface. This film is really important because it allows us to image what we want to etch, but also protect the areas of the metal that we don't want to etch. So here you can see it coming out of the other end,
it's been fully laminated and so that metal is now sandwiched between that photosensitive film. After lamination our next step is digital imaging. With digital imaging you can see here, that film that we just put on the metal surface is going to be hit with UV light, to print the image that we want to etch essentially, that pattern. Here in this video, you'll see the panel that's just been laminated get placed onto that stage with a direct imager and it'll go through that process of printing the pattern. There you can see the operator setting it down, making sure that it's flat. It's going to start moving in that X/Y stage, to start lining up the image with that panel. We're going to get a couple different views here, so you can see what's happening inside
the machine. In this area here, this print head there is used for alignment, so this part here is aligning the image that we're transferring over from a file on the computer to the panel and we want to make sure that we have good alignment between the top and the bottom side. What I didn't mentioned before is that when you're printing, you're only doing one side at a time, so right now it's going to do this top side and eventually we'll see them flip the panel and image the bottom side Aurelia if I can just ask. You have applied the film and this light now has a - projects what you want onto that surface, basically, and it only lights up the areas that you wanted to get exposed, is this correct? Yeah exactly, so you make a drawing using some CAD software and then that's the image, the pattern that you want to etch. So then that gets transferred onto here and with this direct imager it only lights up the
areas that you want to protect essentially, and the rest of the areas as you'll see afterwards gets peeled away, so that you can have your etched dimension or your etched features. As the video continues, you can see, that - so this is helping with the alignment of it. In a second you'll be able to see those three rectangles of blue light, is UV light that is hitting the panel directly and it's imaging at the same time. So they're moving in synchronized motion, to image that pattern onto that laminated metal surface. As you continue watching the operator is flipping the panel over to the other side and so now that panel is ready to be printed on the back side. Using direct imaging technology is really critical as well, because it helps us maintain good alignment between the front and the back, which is important for precise features that are required for bipolar plates.
As we move forward to the next step, after imaging we move on to developing. The next step here for developing, as you can see, that the material on the surface that photosensitive film that's been hit by the light will remain on the material and the rest of it will be washed away. As you can watch on the video here, the panel gets placed into a machine, so it'll be placed on those rollers there you see on the left side over here, it's moving through these chambers and it has a mild alkaline solution that's called a developer. Spray it on both the tops and the bottoms of the panel and it's essentially breaking down the film that wasn't hit by the light, so that it washes away and you're only left with the areas that you want to protect. As it's rolling out of here,
these lighter gray areas are the metal that's peeking through that film. The rest of it, with the majority that's blue greenish, is that protective film that we want to keep on there. So now you see this is the image that we're going to be seeing and etching - that goes on to etching and only that silver area here is going to be attacked by those corrosive chemicals. Understood, so if a chemical comes on there it'll start eating away at those lighter areas we saw on the plate. Yes exactly. So after developing is done the next step is
etching so now we're at like the main portion of it photochemical etching, the thing that we do. So with etching I have an example here and we'll see a couple of different ones after this too, but you can etch different types of designs if you want and you have the ability to etch on both sides. As you can see, generally what happens is you have that etching solution which is that liquid on that top area here, that's hitting both the top and the bottom sides. It's not eating all the way through the metal, which is typically what will happen for bipolar plates, since you have channels that are running through both sides, but they don't meet. They'll have some features that do, but for the most part channels are a certain depth not going all the way through. So as we put it through the etching machine, this machine works very similarly to that developing machine that we just saw. The metal sheet that's ready for etching is placed on the conveyor belt,
it starts to move through the chambers and in the chambers you have that etching solution that is hitting both the top, it's not in the video, but it also can be hitting the bottom and it's eating away at that metal, so it's corroding it away. As it's moving through, obviously this is simplified but you can see that the etchant is causing those holes to open up and those channels to etch as it's moving through. Then when it comes out the other end that darker brown, red-ish chemical you see there is the ferric chloride, that's used to etch the stainless steel in this example. Ok, understood. Can I ask one or two questions around that? This chemical that eats away, how do you control how much it eats away? Doesn't that go really quickly and then you have a hole? Especially when you say you don't want to create a hole, you want only a certain depth of a channel. How do you do that? You control how much you're etching away, by controlling the speed of that conveyor belts movement and also the pressure at which those sprayers are hitting the panels with the etchant.
The higher pressure is going to cause faster etching rate and a slower speed will also cause a faster etching rate, because it's a longer time in the chambers, before it comes out the other end. Sometimes they require a couple of passes, but that's how you would gauge whether you want to etch a hole all the way through or just a channel like you would for a bipolar plate. Okay, and just to understand, how long does that take? Is it like 2s or 3s and then you already have a channel or are we talking minutes, are we talking hours before you get any depth? It's minutes, it really depends on the material that you're etching, some of the materials etch a little bit faster than others, like stainless steel. Those kind of ferrous materials tend to etch a lot faster than titanium for example or molybdenum, but it really depends on the metal. But it's more like minutes. Okay, and how do you ensure, that the one side isn't etched more than the other? Maybe this is such a basic question, but looking at that process I asked myself, how do you ensure the channel that has the same depth everywhere? So with process controls in the process, you have the ability to know how fast you have to run the conveyor, to understand how much is going to etch. With
your etch chemistry for example, with the ferric chloride etchant, when it's like a fresh new bath, it's at its strongest, so it's going to have a much faster rate, so operators would know to etch at a much faster speed, because that etchant is going to be a lot stronger. So there's a lot more of those active ions in there, that are going to be oxidizing that metal surface and it's etching at a much faster rate. With those process controls there is how you get an idea of roughly - okay I understand that for stainless steel I'm running it at this speed and it's going to etch away about 0.5mm - or whatever the case is. So you have a lot of variables there so you have to know how much you've run through that particular solution. That's quite complex chemistry you need to manage there, obviously. Definitely and it's only been
learned after doing it for so many years. It's really important for the bipolar plates that you can maintain those tight depths, because you don't want to have a huge range across one panel or across one plate. So can you say - we saw it on one picture it's called etchant, I quite like that word. What are those? You mentioned ferric chloride or so what are they? So I have a couple more slides here, so I can come back to these.
Here's a general overall chemical reaction that's happening when that material is being oxidized. The etchant is working as an oxidizing agent basically, so that ferric chloride etchant that's like the main component that's driving this reaction and it combines with the metal ions, so that iron substrate you see in the front there. When the etchant is oxidizing the metal surface, it dissolves that away into a soluble salt and then it goes into, basically, the product, which is that reduced chemistry now, which is ferrous chloride now and it's that spent etchant. That has to continuously be moving so you need a lot of agitation
in there which is why the sprayers really help with that, because you need a constant rotation or a constant change in the chemistry hitting the metal surface, so it continues to drive that reaction. Like I mentioned before too, these couple slides here, we have the ability to etch one side if you want, both sides if you want and you can control how much depth you want to do. So you have the ability for a single side etching where you only etch one side. You could do it all the way through if you wanted to potentially or just to a certain depth. You can also do double-sided etching all the way through, similar to that first image we saw, where it had remaining material except here, they continued they met and you have a hole on the panel.
After etching we move on to our next step, which is stripping. At the stripping portion it's basically that etched plate without that film on there because we don't want the protection film anymore it's gone through the process and done what we needed it to. When the material gets stripped, it gets dunked into a tank of an alkaline solution, that's strong enough to remove the rest of that protectant film. It dissolves away the rest of that blue film you see there and when it gets agitated with the sprayer and when it gets rinsed it just washes away from the metal surface, and you're left with your finished piece. So then that brings us to our
last step here, which is inspection. The last step of making a bipolar plate with etching is doing inspection. So here we have a bipolar plate sitting on a optical inspection tool stage and so the way this inspection tool works, is by using light to measure any important features that are important to the application. So you'll measure things like the channel depth, the channel width,
the size of those holes anything like that to make sure that it's to the print and that you're making what you went out to make. And I do have an example of finished plates here to show you. That metal sheet that I pulled out before, once it's gone through that entire process will end up looking something like this. So this is an example of a etched bipolar plate, you can see that there's channels here, like those grooves that are moving through the major center portion of the panel and those through features that you can see at the end here. So you have the ability to type any text or anything like that on here and really you have a range of different features you can add. We have like a much larger size panel too, just so you get an idea of how different panel sizes can be or the types of bipolar plates that are etched. So this one's a whole lot larger, like
three four/times the size of the other one and it has the same general idea for a bipolar plate. You have the channels going through the center, you have the through holes that are here on the side, like these squares, and those holes there. Just to give you an idea. Well okay, that's quite impressive how big that is. Maybe just at that point we were discussing earlier - obviously you
work for Elcon Precision, but your sister company PEI, that is also mentioned here, they make the bigger ones. The expertise is sitting within your organization there. Yeah right. Very impressive Aurelia, just two or three questions to add to this. When you compare etching of bipolar plates, you know that we have other methods of making those channels into bipolar plates. What would you say from a etching point of view is an advantage to this process? Etching definitely has its advantages, when compared to other manufacturing, like metal manufacturing processes, like hydroforming and stamping. One of the key features with
etching is it has a low tooling cost, so you don't have to make a die to get those features. It's just a subtractive process, like we saw it eats away at those channels. Because of that as well it's really easy to make different designs fairly quickly. You're able to just make a new design, transfer that image file over to the direct imager and make a whole new plate without much time in between. In addition to that, you're also able to prototype and move to a volume production fairly quickly, because you're able to create a lot more panels without having to require additional tooling. We also have the ability with etching, to create finer geometries. I just remembered too that we have an additional slide here for that. This is basically
just summarizing what I'm going over. We also have the ability to create finer channel geometries, so we're not dependent on how small a feature can get with a die, since we can just etch that and remove away from the material. We can also do different patterns and different depths on a single side, so we can add complexity to a design without adding additional costs. And with etching you get a flat, burr and stress-free part, so it's essentially ready for stacking without any further processing. Okay, so wow okay. That's very interesting to see that way. Just one particular thing on the cost. I mean we're always talking about the cost of things in the hydrogen industry and we have bipolar plates there, which are part of the stacks, which are one of the more expensive components in that.
So what is it about etching that is expensive? What makes that process expensive - if it is expensive? Or what's like the most expensive step? So one of the most costly parts of doing like a bipolar plate or a chemically etched bipolar plate is really the material, so with etching, like I mentioned before, there's no tooling that you have to worry about adding that cost, but you're really kind of dependent on how expensive a material is. So depending on whether you're using titanium or stainless steel or kind of what the application of the bipolar plate is going to be, that's just going to add a bunch of costs at the start, because they tend to be pretty thick plates as well and that's really what's driving like the high cost for photochemically etched plates. Okay, I have two more questions and one is about - I mean these are probably aggressive chemicals that that you're handling there and can you tell us a little bit about that? I mean obviously that is also something that you need to know how to handle? Do you use a lot of those and can you reuse them or how how does that work? Yeah, so there is a lot of very harsh corrosive chemicals that are required to make etching happen so there's definitely a lot of regulations and laws in place, about how you handle all of that chemical or all those chemical solutions and all that equipment as well. Whenever you're working with an etchant for example, you're able to regenerate to a certain point, by adding additional like chloride ions for example, to turn that ferrous chloride back into ferric chloride, but it can only do that so much to a certain point and then at one point you just have to replenish or create a whole new bath.
So then you produce hazardous waste and there's regulations at the city state and federal levels, especially in the United States and in California, about how much waste that you can be producing and basically getting disposed of, how you get disposed of that waste, if it's diluted enough, for example we have waste water that's produced at the facility through all of the processes that we have and that's dilute enough that we can discharge it to our regional wastewater facility, but it has to be analyzed for any metal ions, to make sure that we're not above any acceptable limits. But with something that's a lot more dense or a lot more hazardous, like the chemical etchant for example, we have to have licensed hazardous waste facilities, that come and pick up that waste for us and dispose of that properly. Okay so that means it's all sort of taken care of, also in terms of regulations to make sure that this can go back to nature.
Yeah, very tightly regulated. Okay the last one Aurelia, because I think we're running out of time. Just when you look at - I mean you you're pushing you're driving this forward and obviously you have seen some changes in the last years. Can you give us a bit of an outlook what development you're seeing in the etching space and what we can expect from there in the next years? Yeah, I think definitely seeing an increase in how complex all of these designs are getting, so all of these bipolar plate designs, adding sometimes two or three depths on a single side and that's luckily really easy and set up for the photochemical etching process, because you're able to get those features and also being able to test new designs I think will be important as we're figuring out what's more efficient. Designs are quickly changing so being able to prototype fairly quickly is important and with photochemical etching you can do that well. I also see volumes growing and with that we have potentially larger format plates like you have here with this larger size one and also more efficient designs and factory automation to help bring costs down and for example like some fuel cell powered aircrafts are in early stages now of what hopefully in the next few years is going to have exponential growth, so there's going to be a higher demand for bipolar plates. Wow okay, that's a very
positive outlook and at least for me I picked up one point and that's the quick prototyping, which I think is very useful for the industry that is evolving, so people now know who can do that and obviously have learned how that is done. Aurelia it's been an absolute pleasure talking to you about this I've really learned a lot and see how these complex words formed into action. Thank you very much for taking the time and thank you for all those who watched. If you like this please give us a like in our channel here or connect to us on social media. Also below the video you will see all the links to the industries involved in this. Thank you very much for watching. Thank you Aurelia for taking the time and we look forward
to have you sometime in the future. Please watch another video. Thank you. Awesome thank you!