A hydrogen fuel cell uses platinum, or a platinum alloy, as the catalyst at its cathode, because platinum is the only metal with enough oxygen-reduction activity and enough corrosion resistance to survive that electrode's acidic, high-potential environment. Cathode platinum content has fallen from 35 mg/cm² of electrode in the 1960s to a fraction of a milligram today, a fifty-year curve heavy-duty trucks now deliberately reverse. What follows traces why platinum does this job, how much a stack uses, what poisons the catalyst and where platinum-free research stands, each figure dated to its source.
Why Does a Fuel Cell Need a Platinum Catalyst?#
A proton exchange membrane fuel cell needs a platinum catalyst at both electrodes because splitting hydrogen at the anode and combining it with oxygen at the cathode run too slowly without one, even at the pair's standard reversible potential of 1.229 V at 25°C. That electrochemistry sits inside the wider set of uses of platinum group metals, one of 22 industrial applications this site catalogs.
The Oxygen Reduction Reaction: Where Most of the Platinum Sits#
Nearly all of a fuel cell's platinum sits at the cathode because the oxygen reduction reaction is kinetically sluggish and carries almost all of the stack's activation overpotential, so the cathode typically holds 75 to 90 percent of total stack platinum. In the acidic, perfluorosulfonic-acid membrane environment at 0.6 to 0.95 V versus a reversible hydrogen electrode, platinum and platinum alloys are the only materials with simultaneously adequate oxygen-reduction activity and corrosion resistance, according to the US Department of Energy's Hydrogen and Fuel Cells Program. That is why thrifting research concentrates on the cathode rather than the anode.
The Hydrogen Oxidation Reaction: Why the Anode Needs So Little#
The anode needs only about a tenth as much platinum as the cathode because the hydrogen oxidation reaction is fast on platinum in acid, historically around 0.03 to 0.05 mg/cm² against 0.1 to 0.4 mg/cm² at the cathode. That speed means the anode has never been the loading bottleneck, and the thrifting effort traced below concentrates almost entirely on the cathode. The anode's platinum still needs protection from carbon monoxide, covered under poisoning below.
How Much Platinum Does a Fuel Cell Use? The Thrifting Curve#
Total platinum-group-metal loading in a state-of-the-art PEM fuel cell stack has fallen by two orders of magnitude since the 1960s and one order of magnitude since the mid-1980s, per the US DOE's Hydrogen and Fuel Cells Program. The decline did not follow a smooth curve: engineers repeatedly traded loading against durability, and the table below names each step to its source.
From 35 mg/cm² to 0.25 mg/cm²: Fifty Years of Loading Reduction#
Table 1 traces the loading curve from 35 milligrams per square centimeter of electrode in the 1960s NASA Gemini program to 0.25 mg/cm² total in 2011, each step named to its source in US DOE Hydrogen and Fuel Cells Program Record #11013 (2 June 2011).
| Era | Total PGM loading | Note | Source |
|---|---|---|---|
| 1960s, NASA Gemini | 35 mg/cm² per electrode | Platinum pressed directly into the membrane | DOE Record 11013 |
| Mid-1980s | About 4 mg/cm² per electrode | Pre-ionomer-impregnation era | DOE Record 11013 |
| 1988, Raistrick (LANL) | 0.35 mg/cm² per electrode | Gas-diffusion electrode impregnated with solubilized ionomer | DOE Record 11013 |
| 1991, Wilson (LANL) | 0.13 mg/cm² per electrode | Catalyst-ink decal transfer | DOE Record 11013 |
| Mid-1990s, Ballard | Under 1 mg/cm² total | Over 3,000 hours durability on reformate | DOE Record 11013 |
| 2011, 3M and GM | 0.25 mg/cm² total (0.19 gPGM/kW) | Beat the DOE 2010 target of 0.2 gPGM/kW | DOE Record 11013 |
Los Alamos National Laboratory had already reached under 0.2 mg/cm² total by the early 1990s, but developers kept higher loadings through most of the 2000s because durability, not activity, was unresolved. The DOE record states the result plainly: total PGM loading "has decreased by 2 orders of magnitude since the 1960s and 1 order of magnitude since the mid-1980s."
Light-Duty vs Heavy-Duty: Why Trucks Use More Platinum, Not Less#
Heavy-duty fuel cell trucks and buses use two to six times more platinum per square centimeter than light-duty cars, because durability and efficiency over 25,000 to 30,000 hours matter more to a truck operator than the metal's cost. Ramaswamy, Kongkanand, Wortman and Gu (General Motors), in the Journal of the Electrochemical Society (3 February 2025), put light-duty cathode loading at 0.05 mg/cm² or less against 0.2 to 0.35 mg/cm² or more for heavy-duty, a 4 to 6 times step. Cullen and coauthors, in a 2021 manuscript archived by the US DOE, pair the same comparison at under 0.125 mg/cm² for light-duty against about 0.3 mg/cm² for heavy-duty, a 2 to 3 times step; the two groups' pairs are never mixed into one ratio.
| Parameter | Light-duty | Heavy-duty |
|---|---|---|
| Cathode platinum loading | 0.05 mg/cm² or less | 0.2 to 0.35 mg/cm² or more |
| Design priority | Minimize platinum cost | Maximize efficiency and durability |
| Rated-power cell voltage | About 0.675 V | Above 0.7 V |
| Durability target | Not the design priority here | 25,000 hours interim, 30,000 hours ultimate |
Heavy-duty vehicles need above 0.7 V per cell for over 50 percent system efficiency, forcing a lower current density and more active area per kilowatt. The same high cathode potential, sustained for 25,000 to 30,000 hours, drives more platinum dissolution and Ostwald ripening than a light-duty cycle does, and temperatures above 90°C accelerate that degradation further. Every factor pushes heavy-duty platinum content up, not down, so the segment growing fastest also thrifts platinum the least.
What Poisons a Fuel Cell's Platinum Catalyst?#
Carbon monoxide poisons a fuel cell's anode catalyst by binding platinum's active sites, a problem only when the hydrogen feed comes from reformate rather than pure hydrogen. A platinum-ruthenium alloy anode restores tolerance: PtRu/C shows the best carbon monoxide tolerance among the alloys tested, with an overpotential loss of only 110 millivolts at 1 A/cm², per a 2008 Electrochimica Acta study corroborated by a 2019 International Journal of Hydrogen Energy study on PtRu and PtRuMo anodes. The two electrodes face different poisons, listed below.
- Anode: carbon monoxide and hydrogen sulfide, both arriving with reformate hydrogen; platinum-ruthenium alloying is the mitigation.
- Cathode: airborne sulfur dioxide, nitrogen oxides and ammonia, arriving from the surrounding air rather than the fuel stream.
Platinum-Free and Low-Platinum Fuel Cell Research#
Researchers have built platinum-group-metal-free fuel cell cathode catalysts from iron and nitrogen pyrolyzed onto a carbon support, sold commercially as a research material under Pajarito Powder's VariPore platform. The US Department of Energy's target for this family is above 0.044 A/cm² at 0.9 V (IR-free), up from a 2015 status of 0.016 A/cm², a gap a 2025 Chemical Science study frames with a new "stability number" descriptor. Durability, not activity, is still the barrier: this catalyst is not deployed in any commercial vehicle fuel cell, and the constraint on replacing platinum is how long it survives, not how fast it starts.
Fuel Cells, Electrolyzers and Other Platinum Applications#
Platinum's fuel-cell role sits alongside a related but distinct hydrogen-economy job in electrolyzers, where a different platinum group metal does the harder work. PEM electrolyzers split water into hydrogen and oxygen using iridium, not platinum, as the anode catalyst that survives the process's higher operating potential, while platinum still coats the cathode and the cell's transport layers.
Related PGM Applications#
Platinum's fuel-cell chemistry connects to two other pages here, plus the application with the most current PGM demand.
- PEM electrolyzers: iridium does the anode's oxygen-evolution work while platinum handles the cathode and transport-layer coatings, detailed in the section above.
- The hydrogen economy overall: how fuel cell and electrolyzer platinum demand fit together, on platinum and the hydrogen economy.
- Catalytic converters: the platinum group metal application with the largest current demand; readers looking for platinum used in a catalytic converter will find automotive exhaust catalysis covered there instead of fuel cells.
Fuel Cell Platinum FAQ#
What catalyst is used in fuel cells?#
Commercial hydrogen fuel cells use platinum, or a platinum alloy such as platinum-ruthenium at the anode, as the electrocatalyst at both electrodes. The cathode runs plain platinum or platinum-cobalt, and the anode adds ruthenium only where the feed contains carbon monoxide.
Why is platinum such a good catalyst for fuel cells?#
Platinum is the standard fuel-cell catalyst because only platinum and platinum alloys combine adequate oxygen-reduction activity with adequate corrosion resistance in a PEM fuel cell's acidic membrane environment. No other metal or alloy has matched that pairing at the potentials a fuel cell cathode sustains.
What are the downsides of a palladium catalyst in a fuel cell?#
Palladium alone is not used as a commercial PEM fuel cell catalyst because platinum and platinum alloys are the only materials found to combine sufficient oxygen-reduction activity with adequate corrosion resistance. DailyPlatinum's sources document no separate list of palladium-specific failure modes beyond that comparison, so none is stated here.
What are platinum's symbol, atomic number and CAS number?#
Platinum has the symbol Pt, atomic number 78 and CAS number 7440-06-4. It is the platinum group metal this page's fuel-cell chemistry runs on, and its full properties are covered on platinum (Pt), element 78.