A PtRu/C catalyst ratio is incomplete unless the specification says whether the platinum-to-ruthenium ratio is atomic or by weight. Because a platinum atom is much heavier than a ruthenium atom, Pt:Ru = 1:1 atomic does not mean equal metal masses. Buyers should also define the total metal percentage on carbon, the loading basis, the electrode side, the application, and the acceptance method. These details determine how much powder is required and prevent different suppliers from quoting chemically different materials under the same short description.

For the broader catalyst-percentage decision, read Pt/C 40%, 60%, and 70%: How to Choose.

What Does PtRu/C Mean?

PtRu/C normally describes a platinum-ruthenium catalyst supported on carbon. It is commonly considered for fuel-cell anodes that need methanol-oxidation activity or improved tolerance to carbon monoxide in hydrogen derived from fuel reforming. TANAKA identifies PtRu-alloy catalysts as standard anode catalysts for reformed-hydrogen fuels because of their CO tolerance. PtRu/C is not automatically required for a PEM fuel cell supplied with high-purity hydrogen, and it should not be selected only from the letters in a product name.

Specification rule: Write the catalyst as, for example: “PtRu/C, Pt:Ru = 1:1 atomic, 50 wt% total metal on carbon.” Do not write only “PtRu/C 50%” or “PtRu 1:1.”

Atomic Ratio and Weight Ratio Are Different

An atomic ratio compares the number of Pt and Ru atoms. A weight ratio compares their masses. Using the Commission on Isotopic Abundances and Atomic Weights standard atomic weights of approximately 195.084 for Pt and 101.07 for Ru, a 1:1 atomic mixture contains about 65.9% Pt and 34.1% Ru by metal mass. Conversely, a 1:1 weight ratio contains approximately one Pt atom for every 1.93 Ru atoms.

The conversions are approximate and are intended to clarify the specification. For production calculations, use the certified Pt and Ru assay for the actual catalyst batch. The nominal atomic ratio does not prove the surface composition, degree of alloying, particle distribution, or electrochemical performance.

Worked Example: 50 wt% Total Metal and 1:1 Atomic Pt:Ru

Assume the catalyst contains 50 wt% total Pt + Ru on carbon and the metal atomic ratio is Pt:Ru = 1:1. Within the metal fraction, approximately 65.9% of the mass is Pt and 34.1% is Ru. The complete catalyst powder therefore contains approximately 32.9 wt% Pt, 17.1 wt% Ru, and 50.0 wt% carbon.

If a drawing requests 0.30 mgPGM/cm² total Pt + Ru, the theoretical catalyst-powder loading is 0.30 ÷ 0.50 = 0.60 mg/cm². That deposit contains about 0.198 mgPt/cm² and 0.102 mgRu/cm². If the requirement is instead 0.30 mgPt/cm², the powder requirement is about 0.911 mg/cm². The same number creates a different material requirement when the loading basis changes.

Define the Loading Basis Before Calculating Powder Mass

State whether the number applies to the anode only or to the whole MEA. PtRu/C is normally an anode catalyst in the applications discussed here. The cathode catalyst and loading should be specified separately. A total stack inventory should be calculated from the finished Pt and Ru loading, coated area, cell count, and accepted process yield—not from wet ink usage alone.

For the complete drawing and loading fields, see How to Specify a Custom Fuel Cell MEA.

Choose PtRu/C According to the Fuel and Anode Reaction

High-Purity Hydrogen PEM Fuel Cells

For high-purity hydrogen, Pt/C is commonly used at the anode because the hydrogen-oxidation reaction is fast. Adding Ru increases formulation and qualification complexity and may not provide a useful benefit when CO exposure is not expected. Confirm the hydrogen specification, purification system, start-stop profile, and target life before replacing a qualified Pt/C anode.

Reformed-Hydrogen PEM Fuel Cells

Carbon monoxide can adsorb strongly on Pt and reduce available reaction sites. PtRu-based anodes can improve CO tolerance, but the required ratio and loading depend on CO concentration, temperature, humidity, pressure, fuel stoichiometry, transient exposure, air-bleed strategy if used, and the complete electrode design. Provide both nominal and maximum contaminant values rather than requesting a generic “CO-tolerant MEA.”

Direct Methanol Fuel Cells

PtRu is widely studied and used as an anode catalyst for the methanol oxidation reaction. DOE-supported NREL work has specifically targeted improved PtRu activity and durability through catalyst-support engineering. The ratio alone is still insufficient: alloying, catalyst surface area, support, ionomer, methanol concentration, operating temperature, water management, and MEA structure affect the final result.

Why Product Codes Must Not Be Used as Ratios

Catalyst manufacturers use proprietary grade names. Numbers within a product code may indicate a family, nominal metal percentage, support, or internal formulation, but there is no universal decoding rule. A code should be copied exactly from the supplier's current data sheet and accompanied by a written description of Pt wt%, Ru wt%, total metal wt%, carbon support, and Pt:Ru ratio basis. Do not interpret a code such as “50” as a 1:1 metal ratio unless the manufacturer explicitly says so.

Ratio Alone Does Not Define Catalyst Performance

Two PtRu/C powders with the same nominal atomic ratio can perform differently. Important differences include Pt and Ru particle size, alloying degree, surface composition, dispersion on carbon, carbon surface area and graphitization, pore structure, impurities, electrochemically active area, and stability under the intended potential cycle. Ink preparation, ionomer-to-carbon ratio, coating method, drying, membrane interface, GDL, and compression further change MEA performance.

·Request a current certificate of analysis showing the Pt and Ru assay and, where applicable, the total metal content.

·Keep the supplier and exact grade fixed during comparison; “PtRu/C 1:1” is not a complete material identity.

·Use matched cell hardware and test conditions when comparing ratios or suppliers.

·Treat catalyst loading verification and electrochemical performance testing as separate acceptance controls.

To confirm the purchased layer scope, read CCM vs MEA: What Fuel Cell Buyers Should Specify.

PtRu/C Catalyst RFQ Checklist

A Practical Sample-Qualification Plan

When no PtRu/C grade is qualified, compare a small controlled matrix. Hold membrane, active area, GDL, compression, cathode, gas conditions, temperature, humidity, and test protocol constant. Adjust each ink sufficiently for its catalyst and carbon fraction, then compare coating quality, metal loading, polarization performance, CO-tolerance or methanol-oxidation behavior as relevant, and durability under a defined cycle.

·Record catalyst lot, Pt and Ru assay, atomic or weight ratio, total metal percentage, ink solids, mixing, coating, and drying conditions.

·Use the actual fuel composition and contaminant level expected in service; a clean-H₂ test cannot prove reformate tolerance.

·Freeze the approved material and formulation in the drawing or bill of materials, with written change control.

H2gatech Engineering Note: Use a Complete PtRu/C Statement

Engineering note: A usable request reads: “Anode catalyst: [manufacturer and grade] PtRu/C; Pt:Ru = 1:1 atomic; 50 wt% total metal on carbon; finished loading stated separately as mgPt/cm² and mgRu/cm²; active area, tolerance, and verification method to be agreed.” H2gatech can then align the catalyst certificate, ink calculation, drawing, coating record, and sample test plan. Final suitability must be verified in the customer's cell hardware and fuel conditions.

Frequently Asked Questions

Is Pt:Ru = 1:1 usually an atomic ratio?

Many technical papers and catalyst specifications use an atomic ratio, but the notation is not safe without the word “atomic” or “molar.” Confirm the basis on the supplier data sheet and certificate instead of assuming it.

Does 1:1 atomic PtRu contain equal masses of Pt and Ru?

No. Based on standard atomic weights, the metal mass is approximately 65.9% Pt and 34.1% Ru. Equal metal masses correspond to approximately Pt:Ru = 1:1.93 by atom count.

Does PtRu/C 50% mean 50% Pt?

Not necessarily. It may mean 50 wt% total Pt + Ru on carbon, but supplier conventions vary. Request the separate Pt and Ru assays and the total-metal definition.

Should PtRu/C be used on both sides of a PEM fuel cell MEA?

Normally no for the applications discussed here. PtRu/C is selected for the anode reaction or contaminant tolerance, while the cathode catalyst is specified separately for oxygen reduction. Confirm both sides on the drawing and quotation.

Can a PtRu/C ratio be selected without knowing the fuel composition?

That is not recommended. Pure hydrogen, reformed hydrogen containing CO, and methanol impose different requirements. Provide nominal and maximum fuel composition, contaminants, operating conditions, and duty cycle before selecting and validating a grade.

Request a PtRu/C and Custom MEA Specification Review

H2gatech supports customized catalyst-coated membranes and membrane electrode assemblies using PtRu/C, Pt/C, Pt black, and application-specific catalyst systems. Send the fuel composition, catalyst grade or target Pt:Ru ratio, total metal percentage, separate Pt and Ru loading basis, active-area drawing, membrane, GDL, sealing requirements, quantity, and acceptance method. Explore H2gatech membrane electrode assembly solutions or contact H2gatech for a specification review.

Technical References

TANAKA Precious Metals — Electrocatalysts for Fuel Cells and Water Electrolysis
U.S. DOE / NREL — Novel Approach to Advanced Direct Methanol Fuel Cell Anode Catalysts
CIAAW — Standard Atomic Weights