# Electrolyzer Electrode Material Selection Guide

> Technical comparison of nickel woven mesh, knitted mesh, nickel foam, and stainless steel electrodes for alkaline water electrolysis. Selection criteria for stack OEMs.


Woven nickel mesh (30-40 mesh, Ni201) is the correct catalyst substrate. Knitted nickel mesh (660-850 g/m2, Ni201) is the correct porous transport layer. Nickel wire (Ni201 annealed) is the correct current collector. One material cannot solve all three positions. Using the wrong material at any position creates a failure mode that limits the entire stack lifetime ,  regardless of how good the catalyst, membrane, or balance of plant is.

> **TL;DR , ** 3 positions, 3 materials: woven Ni201 mesh (catalyst substrate, 30-40 mesh), knitted Ni201 mesh (PTL, 660-850 g/m2, 90-95% porosity), Ni201 wire (current collector, annealed, 0.5-2.0 mm). Ni foam collapses under compression. SS 316L fails via SCC in hot KOH. Specify by position, not by product.

## Three Electrode Positions, Three Material Requirements

**1. Catalyst Support Substrate.** Requires uniform aperture distribution for consistent current density, high surface adhesion for Raney nickel catalyst coating, and a burr-free surface finish to protect the Zirfon or asbestos diaphragm from mechanical puncture. **Recommended:** Woven nickel mesh ,  30-40 mesh per inch, plain weave, 0.25-0.30 mm wire diameter, Ni201 grade, electropolished finish. Ordered aperture geometry ensures every unit cell of the electrode has identical electrical path length and catalyst loading. ASTM B456 and ISO 9044 compliant.

**2. Porous Transport Layer (PTL).** Requires elastic compressibility to maintain electrical contact under 5-15 bar stack clamping force, volumetric porosity above 85% for two-phase electrolyte-gas flow, and recovery from repeated compression cycles over the stack lifetime (60,000+ hours). **Recommended:** Knitted nickel mesh ,  660-850 g/m2 packing density, single jersey knit, 90-95% porosity, Ni201 grade. The three-dimensional loop structure functions as an elastic spring. Interlock (double-knit) variant at 850-1150 g/m2 for large-area stacks above 1 m2 active area where PTL collapse is the primary failure risk.

**3. Current Collector / Lead Wire.** Requires electrical conductivity of 14-18% IACS to carry DC current from the busbar to individual electrode elements, mechanical ductility of minimum 30% elongation for forming and welding, and sustained corrosion resistance in 30% KOH at 80-90 C. **Recommended:** Nickel wire ,  Ni201 grade, annealed temper, 0.5-2.0 mm diameter for internal wiring. Ni201 limits carbon to 0.02% maximum, preventing grain-boundary carbide precipitation (Ni3C) that causes intergranular corrosion in standard Ni200 (0.15% C) after 20,000+ hours. ASTM B162 compliant.

## Head-to-Head Comparison

| Criterion | Woven Ni Mesh | Knitted Ni Mesh | Ni Foam (80-110 PPI) | SS 316L |
|-----------|--------------|-----------------|----------------------|---------|
| Porosity | 35-55% geometric | 85-98% volumetric | 85-98% volumetric | N/A (solid plate) |
| Compressibility | Rigid | Elastic spring-back | Plastic collapse | Rigid |
| Current Uniformity | Excellent (ordered geometry) | Good (elastic contact) | Poor (random structure) | Good (solid) |
| KOH Corrosion at 85 C | Passive (stable Ni(OH)2 film) | Passive | Passive | SCC + Fe leaching into electrolyte |
| Dimensional Stability | Excellent (50,000+ hrs) | Good under compression | Poor (pore collapse) | Excellent |
| Industrial Track Record | 50,000+ hrs proven | 30,000+ hrs proven | Lab-scale only | Not recommended for KOH |
| Cost (relative) | $$ | $$ | $$$ | $ |
| Best For | Catalyst substrate | PTL / spring layer | R&D cells only | External hardware only |

> **Bottom line:** Specify by position. The catalyst substrate, PTL, and current collector are three different engineering problems. Woven Ni201 mesh + knitted Ni201 mesh + Ni201 wire is the matched electrode material set for alkaline electrolyzer stacks targeting 60,000+ hour lifetimes.