Etching of Titanium Bipolar Plates for Hydrogen Energy Applications

Titanium bipolar plates are core multifunctional components inside protonexchangemembrane fuel cells and PEM water electrolyzer stacks for hydrogen energy. As critical conductive and flowdistribution hardware, they undertake electrical conduction, hydrogenoxygencoolant flow distribution, mechanical support for membraneelectrode assemblies (MEA), and heat dissipation within the stack. Operating under strongly acidic, highhumidity and cyclicpotential working environments, bipolar plates demand outstanding corrosion resistance, high electrical conductivity, excellent dimensional consistency and precise microflowfield geometry.

Traditional manufacturing technologies including stamping, hydroforming, CNC milling and laser processing show obvious limitations for thingauge titanium bipolar plates. Stamping and hydroforming introduce heavy mechanical stress, material springback and microdeformation on ultrathin titanium sheets; complex flowfield patterns require expensive hard dies with long development cycles. CNC milling delivers high precision yet suffers low materialremoval efficiency and high cost for mass production. Laser processing creates thermalaffected zones, edge microcracks and surface oxidation, deteriorating subsequent conductivecoating adhesion. Photochemical etching provides a competitive coldprocessing route for titanium bipolar plates, producing burrfree, stressfree doublesided microchannel flow fields, preserving titanium’s intrinsic corrosionresistant metallurgical properties and supporting rapid design iteration for hydrogenenergy stack development.

Material Selection for Etched Titanium Bipolar Plates

Pure titanium grades and selected titanium alloys are primary substrate materials for hydrogenenergy bipolar plates. Commercially pure titanium exhibits superior resistance to acidic electrolyte environments inside PEM stacks compared to ordinary stainless steel, effectively resisting corrosion induced by fluoride ions under longterm operating conditions, extending stack service life and restraining contactresistance drift.

Raw sheet thickness generally ranges from 0.05 mm to 1.0 mm for bipolarplate applications. Titanium features a naturally compact passive oxide layer. Incomingsheet surface quality is extremely critical: surface scratches, rolling defects, uneven oxide film and embedded impurities will cause nonuniform etching rates, resulting in inconsistent channel depth, distorted rib structures and local surface defects. Strict incoming material inspection covering surface finish, material composition and mechanical performance is mandatory. Typical achievable dimensional tolerances for flowfield channels and sealing ribs range from ±0.03 mm to ±0.06 mm. Channel depth can be precisely controlled according to stack design requirements, directly influencing gasliquid masstransfer efficiency inside fuelcell or electrolyzer cells.

StepbyStep Photochemical Etching Workflow for Titanium Bipolar Plates

Titanium possesses strong chemical inertness, requiring specialformulated etching solution and tightlyclosed process parameters different from stainlesssteel etching. Most hydrogenenergy bipolar plates adopt doublesided synchronous halfetching to form anodecathode flowfield channels simultaneously.

Surface Pretreatment and Activation Cleaning

Titanium sheets go through multistage degreasing, alkaline washing and dedicated surface activation treatment to remove rolling oil, fingerprints and original passive oxide film. Residual oxide layers will inhibit uniform chemical reaction and lead to unstable channel geometry. Consistent surface activity across the whole plate guarantees reliable dryfilm photoresist adhesion. Poor cleaning quality causes resist lifting, pattern distortion and local missing flowchannel features.

DualSided DryFilm Photoresist Lamination

Bubblefree dryfilm photoresist is hotlaminated onto top and bottom surfaces of cleaned titanium substrate. Lamination temperature, pressure and conveying speed are precisely calibrated for titanium material characteristics. Microbubbles trapped between photoresist and titanium surface will generate pittype defects on flowchannel ribs after etching. Doublesided lamination enables simultaneous bilateral halfetching, ensuring symmetry and dimensional consistency between anodeside and cathodeside flowfield structures.

UV Exposure and Pattern Development

Highresolution photomask transfers complete bipolarplate graphic information: serpentine / parallel / interdigitated flowchannel arrays, sealing ribs, manifold ports, positioning holes and outer sealing contours. Under UV irradiation, photoresist on nonetching rib and sealingzone areas polymerises and forms stable protective mask layers. Unexposed regions corresponding to flow channels dissolve in developer solution and expose bare titanium surfaces ready for selective dissolution. Photomask design incorporates targeted undercut compensation. For narrow flowchannel ribs, uncontrolled lateral undercut will reduce rib width and impair mechanical strength and conductive contact performance of finished bipolar plates.

Controlled SpecialFormula Chemical Etching

Masked titanium panels are transported through closed spray etching chamber. Custom titaniumspecific etching solution dissolves unprotected metal material and carves out halfetched microchannel flow fields. Etching temperature, solution composition ratio, spray pressure and conveyor velocity are monitored by closedloop control system. Unlike stainlesssteel etching, titanium etching demands stricter chemicalratio stability to balance etching rate, surface roughness and undercut magnitude. Process engineers adjust parameters according to target channel depth and sheet thickness, avoiding overetching of sealing ribs and manifold edges. Uniform channel depth and smooth channelwall surface are critical prerequisites for subsequent conductivecoating deposition.

Photoresist Stripping and MultiCycle HighPurity Rinsing

After target halfetch depth of flow channels is achieved, alkaline stripping agent completely removes residual photoresist mask. Multistage circulating rinsing washes away corrosive chemical residues trapped inside intricate microchannels. Chemical residues remaining on flowfield surfaces will trigger local corrosion and coating delamination in subsequent hydrogenenergy stack operating conditions.

HydrogenEnergyOriented PostTreatment

Postprocessing workflow includes passivation treatment, precision flatness correction, highpurity ultrasonic channel cleaning and surfacedefect inspection. Etched titanium bipolar plates naturally feature burrfree channel walls and sealing edges, eliminating secondary deburring procedures. Since bare titanium will form insulating passive film under stack operating environment, followup surface modification such as conductive PVD coating, carbonbased coating or noblemetal coating is normally implemented to lower interfacial contact resistance and enhance longterm electrochemical stability.

FullItem Quality Inspection for HydrogenEnergy Components

 Key inspection items cover flowchannel depth uniformity, channelrib dimensional tolerance, manifoldport accuracy, flatness, surface roughness, sealingedge integrity and surfacedefect screening. Sampling validation includes coatingcompatibility testing and simulated electrochemical corrosion testing. Automated optical inspection detects tiny channel defects that may affect gasliquid flow and sealing performance. Qualified bipolarplate lots proceed to packaging for fuelcell stack or PEM electrolyzer assembly.

Core Advantages of Etched Titanium Bipolar Plates

First, stressfree and burrfree microflowfield structures. Photochemical etching is cold subtractive manufacturing without mechanical stamping force or thermal input. No residual internal stress exists in titanium substrate, avoiding springback deformation of thin sheets. Smooth burrfree channel walls reduce fluid flow resistance and guarantee reliable stacking sealing performance for largescale stacks.

Second, outstanding design flexibility for complex flowfield patterns. Etching realises serpentine, parallel, interdigitated and mixedlayout flowchannel geometries without expensive hard metal dies. Design modification only requires updating digital photomask files, drastically shortening prototype iteration cycles for newtype hydrogenenergy stack researchanddevelopment, especially suitable for laboratory verification and midbatch production scenarios.

Third, excellent adaptability for ultrathin titanium sheets. Stamping or hydroforming ultrathin titanium below 0.2 mm easily produces material wrinkling, rib distortion and springback. Chemical etching maintains good flatness and dimensional repeatability, supporting lightweight bipolarplate design to improve stack gravimetric power density.

Fourth, superior coatingfriendly surface condition. Etched titanium surfaces possess uniform texture without thermalinduced oxidation layers, laying good foundation for subsequent conductive coating adhesion, helping stabilise low contactresistance performance during longterm stack operation.

Typical HydrogenEnergy Application Scenarios

Etched titanium bipolar plates serve two major hydrogenenergy technical routes. In PEM fuelcell systems, they apply for hydrogenpowered commercial vehicles, portable hydrogen power supplies and stationary distributed powergeneration stacks. In PEM waterelectrolyzer equipment for greenhydrogen production, titanium bipolar plates resist severe anodic acidiccorrosion environments inside electrolyzer cells and become key structural components for megawattlevel hydrogenproduction stacks.

Main Process Challenges and Control Points

Titanium’s chemical inertness constitutes the primary technical difficulty; etching solution formula and process window are much narrower compared with stainlesssteel processing. Slight fluctuation of solution ratio will cause channeldepth inconsistency and poor surface quality. Strict realtime monitoring and adjustment for etchingbath composition are essential. Secondly, undercut compensation for narrow flowchannel ribs requires highprecision photomask design to prevent ribwidth loss. In addition, flatness control for largesize thin titanium sheets needs optimised fixtureconveying system plus dedicated flattening process. Surface contamination and residual chemical agents must be fully eliminated, otherwise they will induce coating peeling and premature stack performance degradation.

Conclusion

Photochemical etching delivers a feasible and reliable manufacturing solution for titanium bipolar plates for hydrogenenergy applications. By avoiding mechanical stress and thermal damage from conventional processing methods, this technology achieves precise doublesided microchannel flowfields while retaining titanium’s inherent corrosionresistant properties. Through strict incomingmaterial screening, specialised titaniumetchingformula control, accurate undercut compensation and complete hydrogencomponentoriented qualityverification workflow, etched titanium bipolar plates satisfy strict requirements of PEM fuelcells and PEM greenhydrogenproduction electrolyzers. As the global hydrogenenergy industry continuously pursues highreliability, lightweight and rapiditerating stack hardware, photochemicaletched titanium bipolar plates will gain broader market adoption in newenergy hydrogenequipment supply chains.