Hydrogen Energy Solutions & PECM

Hydrogen supply system at DLR Cologne. Image rights: Wikimedia Commons

Key Takeaways

1. Hydrogen electrolyzer performance depends heavily on flow distribution
   

2. Microchannel plate geometry & surface quality controls efficiency and durability (embrittlement)
   

3. Feature-to-feature repeatability is critical across large stacks to meet increasing demand
   

4. Conventional manufacturing struggles with dense microfeatures at scale, but PECM offers repeatable feature generation

Alternative energy sources have seen a renewed wave of global interest as environmentalist policies and continued oil supply volatility have driven investors, manufacturers, and consumers towards new energy sources. Solar panels are experiencing continued commercial and consumer growth, new hydroelectric infrastructure continues to be installed at dams globally, wind turbines continue to be deployed, and global electric vehicle usage climbs daily thanks to brands like BYD and Tesla.

However, generated electricity needs to be stored, and clean energy solutions, while adept at producing energy, face challenges with the storage and distribution of that electricity, which is largely grid-constrained. Solar panels only work during the day, and wind can be unpredictable-- and physically containing that energy for further use (be it for transportation or in reserves) limits progress.

Enter hydrogen energy systems: a unique, fossil-fuel-free methodology for storing energy that has:

• Significantly longer storage capabilities than conventional batteries
  

• Direct compatibility with renewable energy methods
  

• Significantly lower emissions than conventional methods (water is the primary byproduct in both fuel cells and combustion)
  

• Improved transport flexibility (pipelines, tanks, shipping)
  

• Higher energy-per-unit mass, enabling usage in weight-sensitive applications
  

Hydrogen is generally produced through electrolysis: the process in which electricity is used to split water into hydrogen and oxygen. This process relies on stacks of repeating cells separated by plates with dense microchannel networks which ultimately control fluid and gas distribution (as well as electrical conduction) across the parts.

These microchannels are absolutely vital to system performance, and the geometry, surface condition, and repeatability of those channel features directly impact both efficiency and scalability. Manufacturing them at scale creates significant engineering challenges, even for advanced manufacturers.

In this article, we'll examine how electrolyzers are designed and manufactured, and explore how PECM’s repeatable microfeature capabilities align with the production of high-performance microchannel plates, ultimately supporting the broader push toward scalable hydrogen infrastructure towards a cleaner global energy future.

Electrolyzer Plates: Design, Usage & Manufacturability

In essence, an electrolyzer is a dense stack of microchanneled plates that allow water (H2O) to flow through those small channels, receive an electrical charge that splits the water into hydrogen and oxygen, and keep the separated oxygen and hydrogen apart so the oxygen can be removed and the hydrogen (holding the stored energy) is held for future usage.

Typically, these stacked plates can number from the dozens to hundreds per system, with microchannel depths and widths in the sub-millimeter ranges, and each plate with dozens or hundreds of these channels, demanding a repeatable and reliable manufacturing process to produce those microfeatures. Materials, depending on the application, can range from stainless steels to nickel alloys.

As previously mentioned, tolerances on these microchannels must be considerably precise in order to facilitate proper flow, purity, and electrical conductivity. Small changes in surface quality or channel depth inconsistencies can lead to uneven reaction rates from poor flow paths, which ultimately lead to efficiency loss or even degradation from a unique phenomenon known as hydrogen embrittlement.

Hydrogen Embrittlement

Hydrogen, being the smallest of the atoms, creates a unique problem when interacting with load-bearing metals over sustained periods: hydrogen can diffuse into microscopic gaps in the micrometer range (caused by surface deformities, irregularities, or poor surface finishing methods) and create embrittlement over time, causing potential mechanical failure of parts. Steels and nickel alloys are particularly sensitive to this process.

As the process continues, the material will often transition from ductile to brittle behaviour, meaning it will be more prone to sudden cracking under stress as opposed to deforming predictably. This can be especially disastrous in high-pressure or cyclic loading environments, as the process can be slow but deliberate. While we are focusing on the issue of hydrogen embrittlement within electrolyzers and hydrogen energy infrastructure, this problem also persists across chemical manufacturing, cryogenic systems for rocket fuel, and certain metal processing environments, among others.

How Legacy Processes Struggle with Electrolyzer Channels

Legacy Process	Strength	Limitation
Stamping	Low cost at scale ✔️	Limited geometry control ❌
CNC machining	High precision ✔️	Slow, tool wear, cost scales poorly ❌
Chemical etching	Fine features ✔️	Undercut, depth limits ❌
Laser processing	Flexible ✔️	Thermal effects, surface integrity ❌

Fact: Most legacy processes struggle to balance precision, repeatability, and scalability simultaneously when tasked with machining dense-featured metal components.

A key issue with legacy processes is their inability to solve all of the key manufacturing challenges with electrolyzer features in a single operation. Photochemical etching, for instance, can excel at machining quality, dense features at scale but often cannot meet certain geometric requirements, such as channels that meet a certain depth range (challenges tend to mount when tasked with machining channels ~50% of the sheet thickness depth). CNC machining methodologies can produce fine features in challenging materials, but may struggle with certain remnants such as burrs, and is generally a nonideal method when tasked with scaling dozens or hundreds of microchannels across potentially hundreds of plates for a single electrolyzer. Laser processing boasts excellent tolerance capabilities in unique geometries and high scalability, but struggles with its own machining remnants due to its use of thermal material removal-- heat-affected-zones change material properties in concentrated, unwanted areas, and recast layers introduce surface defects that can invite hydrogen embrittlement and impede flow.

PECM: Scalable, Repeatable Channel Processing

Pulsed electrochemical machining (PECM) is uniquely positioned to machine microchannel arrays found in hydrogen infrastructure, utilizing its atom-by-atom material removal, material flexibility and parallel processing capabilities.

First, PECM's entirely non-contact and non-thermal methodology for removing the workpiece material comes with a few inherent advantages legacy process generally cannot offer in full:

• No thermal distortion: this includes warping of thin-walled microchannel features

• No heat-affected zone: metallurgical structure stays uniform throughout the part, ensuring consistency across high load cycles of electrolysis

• No possibility of recast layers: melted material via laser or EDM processing may inadvertently re-solidify on the part wall; this does not occur with PECM

• No tool vibration or chatter: PECM is entirely non-contact

• No burrs: workpiece material is removed atom-by-atom and flushed via the electrolytic fluid

Another key benefit for electrolyzer manufacturing is PECM's ability to machine tough-to-machine materials consistently. Hardness is not a direct factor in machinability for PECM, rather, the process cares most about conductivity. This, therefore, allows PECM to machine high-aspect-ratio channels in both copper and Inconel at similar rates.

Arguably the most beneficial application of PECM's capabilities are its high parallelization and repeatability for machining dozens or hundreds of microchannels (feature-to-feature or part-to-part, depending on the plate density). As PECM utilizes an application-specific, multi-tooled cathode infrastructure, it is uniquely suited to allowing hydrogen energy manufacturers to scale the technology for deployment.

PECM Specs Snapshot

While PECM's capabilities differ depending on channel density, aspect ratio, and material type, we can provide a few loose ranges of its capabilities:

• Wall thickness: <0.075mm thick or lower, depending on geometry
  

• Surface finish: down to 0.005-0.4µm Ra possible on many materials
  

• Parallel processing: dozens to hundreds of features simultaneously
  

• Materials: Titanium and nickel alloys, stainless
  

Conclusion: How PECM Enables Scalability for Hydrogen

The increased deployment of renewable energy methods across critical industries will only be enabled by the proper technology to store and transport that energy-- and hydrogen seems to be the ideal option. However, building and scaling the infrastructure to store that energy through electrolysis requires each system to have dozens-to-hundreds of plates with hundreds of parallel, tight-tolerance micro-features each. Manufacturers are not just looking for processes capable of scaling these features, but also retaining the original geometries and surface qualities in the drawings, as a means to deter flow disruptions and hydrogen embrittlement.

While legacy methods may introduce surface irregularities that can lead to embrittlement, PECM's non-contact and non-thermal, repeatable methodology allows hundreds of tight-tolerance microchannels to be machined and finished in a single cathode plunge.

Pulsed electrochemical machining (PECM) offers a unique non-contact and non-thermal method capable of enabling these small features at-scale.