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Economizing on iridium - iridium is an ideal catalyst for the electrolytic production of hydrogen from water

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Hatvani Robert's picture
chief magnet, HATVANI SSR - STRATEGIC SUPPLYCHAIN REDUNDANCY

Raw materials are crucial to the economy. They form a strong industrial base in which a wide range of goods and applications of daily life as well as modern technologies are produced. Reliable...

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  • Nov 6, 2020
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Originally posted here. 

Hydrogen

Hydrogen plays an important role as an energy carrier for sustainable development1-8 and it is also expected to be used as secondary energy in near feature. Hydrogen can also be used as fuel for vehicle and rockets, as chemical, for Ni-H2 electric cell, for direct combustion for heat, and so on. Besides, hydrogen is considered as the lightest element and any leakage of hydrogen gas can be dispersed quickly. Thus, hydrogen is believed as safe as other commonly used fuels for future.

Presently, hydrogen can be economically produced from hydrocarbon reforming, which is neither renewable nor clean from the life cycle point of view. Powered by solar energy, hydrogen can be produced from water via photocatalysis, thermochemical cycles, and water electrolysis. These methods offer renewable and clean production of hydrogen fuel and therefore, have attracted increasing research interests in recent years.

So far, the efficiency of photocatalysis and thermochemical cycles are still too low to be economically competitive. Electrolytic production of hydrogen from water is gradually gaining its importance among the other conventional processes of hydrogen production in the context of renewable energy source utilization and environmentally clean technology. Worldwide research is being carried out to make the process into cost effective.

An electrolyzer is usually subject to massive current values in order to break the water molecules into oxygen and hydrogen. In any electrolytic cell, electrodes are the main physical part of the system. Out of the two types of electrodes, active electrodes get involved in the redox reaction by accumulating or consuming materials of electrodes.

Steel and iron are the most commonly used for electrolysis of water. These electrodes are used as anode and it is sacrificed in electrolysis, as the anode rusts (get oxidized) and the cathode de-rusts (get reduced). Many works have been carried out in stainless steel, brass and aluminum as anodes, due to the familiar corrosion-resistant properties of these materials. Unfortunately, stainless steel releases toxic materials when it decays, brass deposits copper onto the cathode (which accelerates rusting of steel), and aluminum quickly deteriorates.

In this connection, the carbon based electrodes such as carbon and graphite are much more interested due to low cost, good electrical and thermal conductivity, the relatively inert property in alkaline solution compared to metals and also for its porous structure with high purity. The porous structure helps graphite to adsorb hydrogen molecules.

However, the hydrogen production is not systematically studied over the graphite electrode to improve hydrogen production by simple electrolytic process. In the present paper, the effects of electrolyte concentration, temperature, applied voltage and reaction time on the amount of hydrogen gas produced and consequently on the overall electrolysis efficiency is experimentally investigated.

 

Energy research: Economizing on iridium

Iridium is an ideal catalyst for the electrolytic production of hydrogen from water -- but it is extremely expensive. But now a new kind of electrode made of highly porous material does an excellent job with just a hint of iridium.

Today, the royal road to the effective electrolysis of water for the production of hydrogen gas in so called proton exchange membrane (PEM) electrolyzers is to reduce the amount of catalytically highly active but scare nobel metal iridium and at the same time maintain the hydrogen output.

In this type of electrolyzer cell the hydrogen ions migrate via a proton exchange membrane from the oxygen producing anode to the hydrogen producing cathode. The membrane-based technique offers many advantages. The catalyst coated membrane itself is very thin, which makes the electrolytic cell itself small and more versatile, and the absence of a liquid electrolyte means that the whole system requires virtually no maintenance.

Such cells also allow hydrogen production at elevated pressures facilitating and lowing the energy demand for further storage as compressed gas. Finally dynamic load operation is possible with the PEM-technology to react to fluctuations in available current within seconds which renders it suitable for the coupling to renewable energy sources.

But the technology also has one major drawback. Formation of oxygen at the anode is dependent on the use of iridium oxide (IrO2) as a catalyst. IrO2 is a very stable and efficient promoter of this reaction. The problem is that iridium itself is rarer than gold or even platinum, and it is at least as expensive as the latter. Many attempts have been made to find an alternative, but nothing yet tested approaches the long-term stability and catalytic activity of iridium oxide.

 

Just a dash of iridium is enough

Now Ludwig-Maximilian-Universitaet (LMU) in Munich-based chemists involved in the Cluster of Excellence e-conversion, in collaboration with a team at Forschungszentrum Jülich, have succeeded in increasing the yield of hydrogen by a factor of 8 (relative to a commercial reference electrode) by using a novel and highly porous material as catalyst. This success implies that it should be possible to develop an electrolytic cell that achieves the same efficiency as current iridium-based systems but requires only 10% as much iridium.

The new electrode was developed within the framework of the Kopernikus Power-2-X Research Network, which is funded by the Federal Ministry for Education and Research. Its design and performance characteristics are described in a paper published in the journal Advanced Functional Materials. The system makes use of a novel high-porosity oxidic support on which iridium can be evenly dispersed as a thin film, which is easily accessible to water molecules and exhibits high catalytic activity.

 

Loading the catalyst into every single pore

The team first synthesized nanostructured and conductive antimony-doped tin oxide microparticles. These particles provide a highly porous scaffold for binding of the iridium catalyst. They then prepared an aqueous colloidal suspension of iridium oxide nanoparticles, which were loaded into the porous microparticles by means of a solvothermal reaction at high temperature and pressure.

This resulted in the reduction of the iridium oxide particles to metallic Ir. A final thermal oxidation step then led to the formation of iridium oxide nanoparticles within the pores of the metallic scaffold. Subsequent scanning electron microscopy confirmed that every last cavity in the scaffold was coated with a thin film of the catalyst. -- And indeed, electrodes coated with the new material passed the final test with flying colors. In terms of activity, i.e. hydrogen generation, the efficiency per gram of bound iridium exceeded that of a commercially available PEM by no less than eightfold.

As the paper's first author Daniel Böhm points out, the synthesis procedure has one huge advantage. "We can now focus on optimizing each parameter individually. The relevant factors that can be adjusted include the composition, structure and pore size of the material, its conductivity and the level of loading with iridium. In the end we will obtain a highly active, fully optimized system. All the steps in the synthetic route are also compatible with the demands of industrial-scale production, so the approach might be ripe for technical application within a relatively short time."

The material currently used in commercial electrolyzers must meet very high standards in order to guarantee stable operation over many years. Upcoming projects that will address this issue are already planned, says Prof. Dina Fattakhova-Rohlfing of Forschungszentrum Jülich. "First, we want to synthesize even more stable catalysts with the aid of novel nanoarchitectures. And then we would like to investigate how the properties of these materials behave when subjected to operational conditions over longer periods of time."

 

SOURCE

Efficient OER Catalyst with Low Ir Volume Density Obtained by Homogeneous Deposition of Iridium Oxide Nanoparticles on Macroporous Antimony-Doped Tin Oxide Support. Daniel Böhm, Michael Beetz, Maximilian Schuster, Kristina Peters, Alexander G. Hufnagel, Markus Döblinger, Bernhard Böller, Thomas Bein, and Dina Fattakhova-Rohlfing. Adv. Funct. Mater. 2019, 1906670

SOURCE

Alkaline water electrolysis is one of the easiest methods for hydrogen production that has the advantage of simplicity. The major challenges in the water electrolysis are the reduce energy consumption, cost and maintenance and to increase reliability, durability and safety. In this regard, the electrolytic production of hydrogen is systematically studied by commercially available graphite electrode at room temperature. The experimental results showed the rate of production of hydrogen gas was significantly affected when the reaction parameters such as effect of electrolyte concentration, temperature, applied voltage and reaction time are varied. From the experimental results, it has been found that graphite is a good choice for the production of maximum hydrogen compared to various other electrodes.

Discussions
Matt Chester's picture
Matt Chester on Nov 6, 2020

Thanks for sharing these exciting developments, Hatvani-- do you have any estimate for how long it'll be before these types of breakthroughs might find their way to commercialization? 

Hatvani Robert's picture
Hatvani Robert on Nov 10, 2020

Breakthroughs always take their time. The longest journey begins with the first step. The decision to use our resources more sustainably is a done deal. Change is always an opportunity.

The task now is to implement the options available to us as efficiently as possible. At an economic level, sooner or later the more efficient solution will always prevail - it has never been different. Commercialization has a lot to do with perception.

The process of commercialization plays on many levels and is usually more complex than perception. I am of the opinion that the element of perception will come into play in the foreseeable future and that it can and will have a significant impact on commercialization.

Ultimately, costs and effort are compared on the test bench. I am aware that the full costs are only very rarely summed up in full. Energy is the most essential thing we use. As soon as more efficient solutions are available, we will use them. For this purpose, transparency for costs and effort for all energy expenses are more than essential.

Bob Meinetz's picture
Bob Meinetz on Nov 7, 2020

Hatvani, let's assume 100%-efficient electrolysis is attainable. Has there been any thorough energy or cost analysis showing hydrogen from renewables could be cost-competitive with hydrogen from methane, even in that idealized scenario?

Seems that would be a good place to start. If not, there are hundreds of $millions being wasted chasing a technology with no legitimate purpose.

Hatvani Robert's picture
Hatvani Robert on Nov 10, 2020

An efficiency of 100% is comparable to the speed of light - too good to be true. In nominal operation, ITER will generate around 500 MW of fusion power for pulses of 400 seconds and longer. Typical plasma heating levels during the pulse are expected to be around 50 MW, so the power gain (Q) is 10. During the pulse, the ITER plasma thus generates more energy than it consumes. I think it's a matter of perspective. All known Fosil energy sources are limited - up to a certain point - water is not.

The costs for the expansion of the necessary infrastructure for the production of hydrogen on a large scale are absolutely realizable. The costs are so high because changes always require investments and the initial costs relate primarily to the infrastructure. As soon as this exists, energy can be stored in very large quantities on a sustainable basis, which will bring great advantages, especially in the sustainable energy sector.

Methane is simply a carbon atom linked to four hydrogens (CH4). Those carbon-hydrogen bonds are intermediate in stability between combustible hydrogen-hydrogen bonds and the extremely stable molecules that form from its burning, carbon dioxide and water.

In steam-methane reforming, methane reacts with steam under 3–25 bar pressure (1 bar = 14.5 psi) in the presence of a catalyst to produce hydrogen, carbon monoxide, and a relatively small amount of carbon dioxide. Steam reforming is endothermic - that is, heat must be supplied to the process for the reaction to proceed.

Methane has a much higher energy density. In the end it is a question of availability and the energy expenditure. The focus lies definitely on the efficiency component, we can only influence availability to a limited extent. Through technology and improved processes, we can significantly increase efficiency.

Bob Meinetz's picture
Bob Meinetz on Nov 10, 2020

Hatvani, I have yet to see evidence that nuclear fusion will be remotely economical or practical within the next 40 years.

Thus, hydrogen will continue to be made by steam-reforming methane, and my point was this: even if 100% efficiency was possible, there is no thermodynamic or environmental advantage to converting methane to hydrogen. It will always be less efficient, and create more CO2 emissions, than simply burning methane to generate electricity.

?

Hatvani Robert's picture
Hatvani Robert on Dec 3, 2020

You are right - in steam-methane reforming, methane reacts with steam under 3–25 bar pressure (1 bar = 14.5 psi) in the presence of a catalyst to produce hydrogen, carbon monoxide, and a relatively small amount of carbon dioxide. Steam reforming is endothermic—that is, heat must be supplied to the process for the reaction to proceed.

Facts are - that Hydrogen production is the family of industrial methods for generating hydrogen gas. As of 2020, the majority of hydrogen (∼95%) is produced from fossil fuels by steam reforming of natural gas, partial oxidation of methane, and coal gasification. Other methods of hydrogen production include biomass gasification and electrolysis of water.

The production of hydrogen plays a key role in any industrialized society, since hydrogen is required for many essential chemical processes. As of 2019, roughly 70 million tons of hydrogen are produced annually worldwide for various uses, such as, oil refining, and in the production of ammonia (Haber process) and methanol (reduction of carbon monoxide), and also as a fuel in transportation. 

Hydrogen made by the electrolysis of water is now cost-competitive and gives us another building block for the low-carbon economy

Generating an extra unit of electricity via PV or wind has no cost. One implication of the growth of renewables is that open-market power prices will therefore tend to fall. As the economists say, prices tend to converge on the marginal cost of production. We are seeing this today in electricity markets. This has profound effects.

Hydrogen from electrolysis is key

Very roughly, a new electrolysis plant today delivers energy efficiency of around 80%. That is, the energy value of the hydrogen produced is about 80% of the electricity used to split the water molecule. Steam reforming is around 65% efficient.

Focus on Hydrogen Storage Challenges

For transportation, the overarching technical challenge for hydrogen storage is how to store the amount of hydrogen required for a conventional driving range (>300 miles) within the vehicular constraints of weight, volume, efficiency, safety, and cost. Durability over the performance lifetime of these systems must also be verified and validated, and acceptable refueling times must be achieved. Requirements for off-board bulk storage are generally less restrictive than on-board requirements; for example, there may be no or less-restrictive weight requirements, but there may be volume or "footprint" requirements. The key challenges include:

Weight and Volume. The weight and volume of hydrogen storage systems are presently too high, resulting in inadequate vehicle range compared to conventional petroleum fueled vehicles. Materials and components are needed that allow compact, lightweight, hydrogen storage systems while enabling mile range greater than 300 miles in all light-duty vehicle platforms.

Efficiency. Energy efficiency is a challenge for all hydrogen storage approaches. The energy required to get hydrogen in and out is an issue for reversible solid-state materials. Life-cycle energy efficiency is a challenge for chemical hydride storage in which the byproduct is regenerated off-board. In addition, the energy associated with compression and liquefaction must be considered for compressed and liquid hydrogen technologies.

Durability. Durability of hydrogen storage systems is inadequate. Materials and components are needed that allow hydrogen storage systems with a lifetime of 1500 cycles.

Refueling Time. Refueling times are too long. There is a need to develop hydrogen storage systems with refueling times of less than three minutes over the lifetime of the system.

Cost. The cost of on-board hydrogen storage systems is too high, particularly in comparison with conventional storage systems for petroleum fuels. Low-cost materials and components for hydrogen storage systems are needed, as well as low-cost, high-volume manufacturing methods.

Codes and Standards. Applicable codes and standards for hydrogen storage systems and interface technologies, which will facilitate implementation/commercialization and ensure safety and public acceptance, have not been established. Standardized hardware and operating procedures, and applicable codes and standards, are required.

Life-Cycle and Efficiency Analyses. There is a lack of analyses of the full life-cycle cost and efficiency for hydrogen storage systems.

Facts

A fact is that the efficiency of electrolysis is determined by the amount of electricity used to produce an amount of hydrogen. Depending on the method used, the efficiency of water electrolyser is currently in the region of 60 to 80 %

Electrolysis is a promising option for hydrogen production from renewable resources. Electrolysis is the process of using electricity to split water into hydrogen and oxygen. This reaction takes place in a unit called an electrolyzer. Electrolyzers can range in size from small, appliance-size equipment that is well-suited for small-scale distributed hydrogen production to large-scale, central production facilities that could be tied directly to renewable or other non-greenhouse-gas-emitting forms of electricity production.

Hydrogen production via electrolysis may offer opportunities for synergy with variable power generation, which is characteristic of some renewable energy technologies. For example, though the cost of wind power has continued to drop, the inherent variability of wind is an impediment to the effective use of wind power. Hydrogen fuel and electric power generation could be integrated at a wind farm, allowing flexibility to shift production to best match resource availability with system operational needs and market factors. Also, in times of excess electricity production from wind farms, instead of curtailing the electricity as is commonly done, it is possible to use this excess electricity to produce hydrogen through electrolysis.

Bob Meinetz's picture
Bob Meinetz on Dec 4, 2020

"A fact is that the efficiency of electrolysis is determined by the amount of electricity used to produce an amount of hydrogen. Depending on the method used, the efficiency of water electrolyser is currently in the region of 60 to 80 %..."

Electrolysis of 80% efficiency releases copious quantities of chlorine gas into the atmosphere. Though atomic chlorine isn't a greenhouse gas, it does react with ozone, depleting the atmospheric ozone layer. Chlorine-free electrolysis is possible, however, its efficiency to date is < 30%.

Producing hydrogen gas from electrolysis for industrial processes might be practical if it became cost-competitive with steam-reformed methane. But converting renewable, "green" electricity to useful energy for consumer use is a multi-step process, in which electrolysis plays a relatively minor part. By only considering electrolysis, we're ignoring the energy cost of refrigerating it, of compressing it to > 70 MPa so it can be used in fuel-cell vehicles, of transporting it to fueling stations. The efficiency of proton exchange membrane (PEM) fuel cells varies dynamically with the rate of consumption; one study cites a best possible case of 50% efficiency.

Without a thorough, well-to-wheels emissions and cost analysis of "green" hydrogen showing it's both environmentally and economically superior to other fuels, we could be wasting $billions and years on a business model that is leading us down the wrong path.

Hatvani Robert's picture
Thank Hatvani for the Post!
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