We’re Seeing A Great Deal Of Progress In Electrocatalysis

OVERVIEW

Fuel cell technology is one of the energy sources of the future. It has greater potential than wind or solar and is the only commercial technology in existence today that is capable of replacing the internal combustion engine (ICE). The advantage of fuel cells is that they have a very high efficiency (currently 60% vs 20% for ICEs), which means that out of the 33 KWh of chemical energy found in a kg of hydrogen, over 20 KWh of it can be extracted and used, while a car can only extract 6 KWh from the 33 KWh of chemical energy in a gallon of gasoline. This after a hundred years & trillions of $ spent on engine development & incrememntal improvements. Additionally, fuel cells have no moving parts and, as a result, are far less complex to manufacture and therefore can potentially be more robust and durable. They also have a higher power density than ICE systems and considering that they’re still in the early stages of development, prices will continue to fall, power density will continue to increase, while system durability will also increase exponentially.

Catalyst Coated Membrane

Catalyst Coated Membrane

The biggest limitation for fuel cells thus far is something called the Catalyst Coated Membrane (CCM), which is responsible for the oxidation and reduction of hydrogen and oxygen respectively. This is the process that produces electricity. The CCM is an electrical insulator or barrier that looks like your ordinary kitchen plastic wrap. It blocks electrons but allows protons to pass through and travel from anode to cathode. Unfortunately, the CCMs in the market today all make use of platinum as the chief catalyst but that very platinum is in actual fact the most expensive and least durable component of fuel-cell technology! It becomes rather obvious therefore that finding a different type of catalyst that is cheaper and more durable that platinum would no doubt lead to the end of the world’s reliance on oil, forever. This is the energy breakthrough we’re all waiting for. The CCM is the key to the success of fuel cells.

I’m of the opinion that such a platinum-free or platinum-reduced catalyst has already been developed and that it’s just a matter of time before somebody finds out and does the necessary testing & prototyping to commercialize it. There are a number of entities, institutions, universities, and companies researching the possible alternatives to platinum, some are more well know than others while others have made less progress than others, but it’s still progress nonetheless. Below are some of the most promising:

Nickel
Graphene
Gold
Molybdenum
Cellera
Imitating The Hydrogenase Enzyme

NICKEL

DOE’s Brookhaven National Laboratory – Created a Nitride-stabilized Platinum/Nickel (PtNiN) Core for the Oxygen Reduction Reaction (ORR) at the cathode. The ORR is the reaction where oxygen collects an electron from hydrogen and forms water at the cathode side of the fuel cell. This catalyst is more durable than Pt/C and has 10 times higher activity per square centimeter.

Nitride Stabilized NiPt Core

Nitride Stabilized PtNi Core

The nitrogen slows down the rate at which nickel dissolves in the acidic environment. The high ORR activity and durability of the PtNiN catalyst is attributed to the Ni nitride core, which modifies the behavior of the Pt shell by inducing both geometric and electronic effects. After tests of 35,000 cycles, there was little change in both the electrochemical surface area as well as the specific & mass activity . The Lab is still conducting further research on this catalyst.

DOE’s Argonne National Labs & Lawrence Berkeley Labs.  A Platinum/Nickel (PtNi) dodecahedron catalyst for ORR. Uses 85% less platinum, has more than 30 times the catalytic activity of platinum, & a synthesis time of only 2 hours. The platinum nickel nanoframes showed no decrease in activity after 10,000 cycles, demonstrating high durability even in high heat. The 2011 version of the catalyst was an order of magnitude higher in activity than the target set by the DOE for 2017. As the next step, Argonne scientists are scaling up the catalyst production for testing in a fuel cell to understand how the nanoframe catalyst will work in practical applications. They also collaborated with China materials science division.

Formation of open architecture of the Pt3Ni nanoframes.

Formation Of The Open Architecture in Pt3Ni Nanoframes.

Pt3Ni open architechture reacting with oxygen.

Pt3Ni Open Architecture Reacting With Oxygen.

In 2014, a new version of this PtNi nanoframe catalyst, licensed to GM, achieved the highest specific and mass activity for the ORR ever measured for practical nanoscale electrocatalysts. A new synthesis method (solvo-thermal synthesis) creates an open architecture of the Pt3Ni nanoframes that enables reactants to have access to both the internal and external catalyst surfaces. Addition of protic ionic liquid led to a 36-fold enhancement in mass activity and 22-fold enhancement in specific activity compared with Pt/C. The high stability & durability is ascribed to the new electron structure resulting from the new Pt skin created during synthesis.

GRAPHENE

South Korea’s Case Western University – Developed a boron carbonitride (BCN) graphene electrocatalyst made with a cheap scalable method of heat annealing graphite oxide. Has higher cathode ORR activity than Pt/C, and is very durable & heat resistant.

Case Western Reserve University and University of North Texas – They made edge-halogenated graphene nanoplatelets as efficient metal-free eletrocatalysts for ORR; a cheap, ball milled, XGnP graphene cathode catalyst (with X standing for either Cl, Br, or I) that’s more tolerant to carbon monoxide & more durable over thousands of charge cycles than platinum. By simply ball-milling griphite flakes in the presence of a halogen such as chlorine (Cl2), bromine (Br2) or iodine (I2), they produced high quality graphene nanoplatelets with halogen edges in a much more cost effective way than chemical vapor deposition (CVD). Fluorine was not used is it is too toxic to humans. The catalyst generates 133% more current than platinum & is also not poisoned by methanol in direct methanol fuel cells. Maintains 87.4% of current after 10,000 cycles vs 62% for Pt/C. The catalyst was not tested in a complete fuel cell system, rather, tests were conducted in an alkaline environment. This is not directly comparable to the acidic environment found in platinum-containing fuel cells such as PEMFC and DMFC.

Ball Milling Graphene

Ball Milling Graphite To Produce Graphene Nanoplatelets

GOLD

DOE’s Brookhaven National Laboratory (BNL) –  A Platinum/Palladium/Gold (PtPdAu) catalyst that uses one tenth the amount of platinum in ORR. This is the same catalyst being used by Toyota under license. The tech was also licensed to N.E. Chemcat Corporation of Japan. Uses 10 grams of platinum per car and less than 20 grams palladium. In 2014, BNL discovered that stabilizing the core multi-metallic group with nitride increases durability to a point were there’s no significant loss is in activity after 200,000 cycles. In testing, the palladium nanoparticles only raised the efficiency by 4%, while the gold raised it 21. 16%. The physical mixture of gold and palladium had a 24. 48% increase, while the alloy of gold and palladium raised the maximum power by 43. 67%. Not only is the alloy’s percent increase significantly larger than that of gold, it is considerably cheaper too, as gold is close to $1800 per ounce, while palladium is just $700 per ounce.

Toyota FCV Interior

Toyota FCV Interior

MOLYBDENUM

DOE’s Brookhaven National Laboratory – For hydrogen production. Cheap & easy-to-make cobalt-molybdenum-nitride as well as nickel-molybdenum-nitride catalyst, that costs $52 per kg.

University of Carlifonia, Berkely’s Associate professor, Christopher Chang  – MoS2 catalyst to replace platinum in hydrogen production.

EPFL’s Daniel Merki – MoS2 catalyst to replace platinum in hydrogen production.

DOE’s Brookhaven National Laboratory – Biomass derived electrocatalytic composites for hydrogen production. MoSoy (Molybdenite Soy bean compound).  Highly durable in corrosive acidic solution tested over 500 hours. Not as fast as Pt/C, but just as fast when supported on graphene sheets. These catalysts are produced by the solid-state reaction of soybeans and ammonium molybdite. Ammonium molybdate was dissolved in water, followed by the addition of ground soybean powder. The mixture was ultra-sonicated, dried and calcined at 800 ˚C under Argon in a tube furnace. A dark grey powder (MoxSoy, x: weight ratio of the Mo precursor to soybean powder) was obtained. This study unambiguously provides evidence that a cheap and earth-abundant transition metal such as molybdenum can be turned into an active catalyst by the controlled solid-state reaction with soybeans. Most importantly, the preparation of the MoSoy catalyst is simple and can be easily scaled up. Its long term durability and ultra-low capital cost satisfy the prerequisites for its application in the construction of large scale devices. Twin-sister high school students contributed to the research as part of an internship.

MoSoy

MoSoy – Molydenum & Soybean.

CELLERA

Cellera – An Israel upstart creating Alkaline Anion Exchange Membrane fuel cells (AAEMFC) that are unique in that instead of a liquid electrolyte, they have a lightly alkaline solid electrolyte that allows for the use of light weight aluminium and is platinum free. Instead of transporting protons from anode to cathode, this fuel cell transports Hydroxyl ions from cathode to anode. Uses a phthalocyanine catalyst at the cathode & a combination of nickel & silver at the anode. This company is funded by Vodaphone and has commercialization agreements with the telecoms company, Commscope.

Cellera

Cellera

IMITATING THE HYDROGENASE ENZYME.

To make fuel cells less expensive, some researchers turned to natural hydrogenase enzymes for inspiration, such as those found in termite guts and E-coli. These enzymes break hydrogen for energy in the same way a fuel cell would, and not only can they split hydrogen apart, then can also join it back together. But while conventional fuel cell catalysts require expensive platinum, natural enzymes use cheap iron or nickel at their core. Hydrogenases are more catalytic than platinum. In fact, they’re the most active molecular catalysts for hydrogen production and oxidation.

In nature, the enzyme can split hydrogen into electron plus proton, & reverses the process all at room temperature & pressure or ambient conditions & using abundant metals such as iron/nickel. Looks like God did it already. Let’s just copy him. Could we use the enzyme itself as a catalyst for an energy storage system? It turns out that these enzymes are difficult to extract and produce in quantity, and they are not terribly stable or survivable outside the specific natural environments to which they are accustomed. So the naturally occurring enzymes would not really be suited for an industrial application.  It is possible, however, to imitate the “active site” of the enzyme, or the part of the enzyme that actually performs the catalytic reaction. Through a technique called protein film voltammetry, the catalytic action of these enzymes can be extensively analysed and described, while studies involving protein crystallography provide insight into the structure of the active site.

Hydrogenase Fuel Cell Design

An Hydrogenase Enzyme in Action

Essentially, the active site of the enzyme consists of a metal atom at the hub of several molecular “spokes” (technically called “ligands”) to which organic compounds known as amines are appended. One feature of amines—organic molecules built around a nitrogen atom—is their strong tendency to bond with protons. In the catalytic action of the enzyme, the amines essentially grab a proton or H+ from an H2O molecule and then combine it with an H- like a relay runner grabbing a baton from her predecessor and then passing it on to her successor. Together the H+ and H- combine to form a molecule of hydrogen gas, or H2. The amines work in tandem with the metal atom (nickel or iron). While the amine grabs one proton, the nickel or iron atom adds two electrons to the second proton. As a result, the two hydrogen atoms end up with opposite charges—the one grabbed by the amine is positive, while the one held by the nickel is negative. The opposite electrical charges of the two hydrogen atoms cause them to mutually attract and ultimately to bond together as hydrogen gas, or H2. 

Japan’s Seiji Ogo of Kyushu University – A catalyst based on the hydrogenase enzyme, Citrobacter H2ase S-77 for hydrogen oxidation at the anode. Citrobacter H2ase S-77The heat resistant enzyme was discovered by professor Ogo and his team in volcanic lava after it was spewed out by a volcano eruption.

Some of the interesting things about this enzyme’s molecular design is the incorporation of sulfur, not phosphorous, and the use of both iron and nickel. The catalyst they produced has over 600 times the mass activity of Pt/C plus twice the current density & twice the power density.  Though H2ases are not new, their application to the polymer electrolyte fuel cell (PEFC) has not been possible until now because they deactivate upon exposure to oxygen since sometimes oxygen can seep through the membrane, travelling from cathode to anode. H2ase S–77, however, remains active in the presence of oxygen.

DOE’s Pacific North West Laboratory – Hydrogen Oxidation & production using nickel and or iron. They designed an iron/nickel-based fuel cell & hydrogen production catalyst based on the internal structure of a hydrogenase enzyme. After many tweaks to the synthetic design, they built a catalyst capable of creating hydrogen gas at the rate of 33,000 molecules per second. Adding water to the solution brought the rate up to over 100,000 molecules per second. This compares to the reported rate for natural hydrogenases—as they occur in actual microbes—of 9,000 molecules per second. So the synthetic version appears roughly ten times as fast as Nature’s. PNNL is now working on making the catalyst a little more efficient.

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