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U Glasgow chemists develop new electrolyzer architecture for H2 production 30X faster than current electrolyzers at equivalent platinum loading

Chemists from the University of Glasgow (Scotland) have developed a new method for hydrogen production that is 30 times faster than current state-of-the-art proton exchange membrane electrolyzers at equivalent platinum loading. The process also solves common problems associated with generating electricity from renewable sources such as solar, wind or wave energy. A paper on their method is published in the journal Science.

The method uses a recyclable redox mediator (silicotungstic acid) that enables the coupling of low-pressure production of oxygen via water oxidation to a separate, catalytic hydrogen production step outside an electrolyzer that requires no post-electrolysis energy input. This approach sidesteps the production of high-pressure gases inside the electrolytic cell (a major cause of membrane degradation) and essentially eliminates the hazardous issue of product gas crossover at the low current densities that characterize renewables-driven water-splitting devices.

The new method allows larger-than-ever quantities of hydrogen to be produced at atmospheric pressure using lower power loads, typical of those generated by renewable power sources. It also solves intrinsic safety issues which have so far limited the use of intermittent renewable energy for hydrogen production.

Of the alternative methods for H2 production that are not linked to fossil resources, the electrolysis of water stands out as a mature, scalable technology for which the only required inputs are water and energy (in the form of electricity). Hence, if the energy source is renewable, H2 can be produced sustainably from water using electrolysis.

Renewable energy inputs tend to be sporadic and fluctuating, and thus the systems that are developed to harness this energy and convert it to H2 [such as proton exchange membrane electrolyzers (PEMEs), solar-to-fuels systems, and artificial leaves] must be able to deal with varying energy inputs effectively and have rapid startup times. At the low power loads that are characteristic of renewable power sources, the rate at which H2 and O2 are produced may in fact be slower than the rate at which these gases permeate the membrane. At the very least, this will severely affect the amount of hydrogen that can be harvested from such devices, and in extreme cases could give rise to hazardous O2/H2 mixtures. The PEME is the most mature technology cited for renewables-to-hydrogen conversion, but prevention of such gas crossover at low current densities remains a challenge.

… There is thus a need to develop new electrolyzer systems that can prevent product gases from mixing over a range of current densities and that make more effective use of the precious metal catalysts they employ, in order to make renewables-to-hydrogen conversion both practically and economically more attractive.

—Rausch et al.

The research team was led by Professor Lee Cronin of the University of Glasgow’s School of Chemistry.

The process uses a liquid that allows the hydrogen to be locked up in a liquid-based inorganic fuel. By using a liquid sponge known as a redox mediator that can soak up electrons and acid we’ve been able to create a system where hydrogen can be produced in a separate chamber without any additional energy input after the electrolysis of water takes place. The link between the rate of water oxidation and hydrogen production has been overcome, allowing hydrogen to be released from the water 30 times faster than the leading PEME process on a per-milligram-of-catalyst basis.

—Professor Cronin

F1.large
A schematic of silicotungstic acid–mediated H2 evolution from water. At the anode, H2O is split into O2, protons, and electrons, while the mediator is reversibly reduced and protonated at the cathode in preference to direct production of H2. The reduced H6[SiW12O40] (dark blue) is then transferred to a separate chamber for H2 evolution over a suitable catalyst and without additional energy input after two-electron reduction of the mediator to H6[SiW12O40]. Click to enlarge.

The use of a redox mediator that can be reversibly reduced in an electrolytic cell (as water is oxidized at the anode) and then transferred to a separate chamber for spontaneous catalytic H2 evolution leads to a device architecture for electrolyzers that has several important advantages, the team noted.

  1. It allows the electrochemical step to be performed at atmospheric pressure, while potentially permitting H2 to be evolved at elevated pressure in a distinct compartment.

  2. Virtually no H2 is produced in the electrolytic cell itself, which (taken with the feature above) obviates the need to purge H2 from the anode side of the cell and could significantly reduce ROS-mediated membrane degradation and the possibility of explosive gas mixtures forming at low current densities or upon membrane failure.

  3. H2 evolution from such a system is no longer directly coupled to the rate of water oxidation, and thus the decoupled H2 production step can be performed a rate per milligram of catalyst that is more than 30 times faster than that for state-of-the-art PEMEs.

  4. The hydrogen produced has the potential to have an inherently low O2 content, both on account of its production in a separate chamber from water oxidation and by virtue of the fact that the reduced mediator reacts rapidly with O2 in solution. This final point could render the H2 produced suitable for applications requiring high-purity H2 such as fuel cells or the Haber-Bosch process, without the need for post-electrolysis purification or built-in recombination catalysts.

Rausch
Comparison of the rate of H2 production possible with silicotungstic acid–mediated electrolysis and a selection of leading PEMEs from the current literature. Literature values are based on the highest rate of H2 production reported in those works. A table with more examples and a full description of how these metrics were calculated can be found in the paper’s supplementary materials. Rausch et al. Click to enlarge.

The research was produced as part of the University of Glasgow Solar Fuels Group, which is working to create artificial photosynthetic systems which produce significant amounts of fuel from solar power.

Around 95% of the world’s hydrogen supply is currently obtained from fossil fuels, a finite resource which we know harms the environment and speeds climate change. Some of this hydrogen is used to make ammonia fertilizer and as such, fossil hydrogen helps feed more than half of the world’s population. The potential for reliable hydrogen production from renewable sources is huge. The sun, for example, provides more energy in a single hour of sunlight than the entire world’s population uses in a year. If we can tap and store even a fraction of that in the coming years and decrease our reliance on fossil fuels it will be a tremendously important step to slowing climate change.

—Professor Cronin

The University of Glasgow’s Dr. Greig Chisholm, Dr. Mark Symes and Benjamin Rausch also contributed to the paper.

Resources

  • Benjamin Rausch, Mark D. Symes, Greig Chisholm, and Leroy Cronin (2014) “Decoupled catalytic hydrogen evolution from a molecular metal oxide redox mediator in water splitting” Science 345 (6202), 1326-1330. doi: 10.1126/science.1257443

Comments

Davemart

A perhaps unglamorous but critical enabler of hydrogen from renewables, it would seem.

gorr

I always thought that storing and using energy in the form of hydrogen is better and cheaper than using batteries. Hurry-up hydrogen, we need you, why waiting so long. Actually more than 99.9% of the energy of the sun and wind is not tap. Please produce and use hydrogen with this new method and kill gasoline.

SJC

A 50% efficient electrolyzer and a 50% efficient fuel cell makes a 25% efficient "battery", versus 90% for lithium ion.

Davemart

@SJC:
50% efficient electrolysis?
Try over 80% if heat is utilised, 70% if not.

HarveyD

Are solar cells, electrolizer and FC efficiencies that important when both inputs (sunlight and water) are plentiful and free?

Even at 50% efficiency, we have enough sunlight and water to produce 10,000+ times the clean renewable energy needed?

If this can be reproduced at reasonable cost, in small and large quantities; solar-wind RE, BEVs and FCEVs will have a bright future.

CPPs, NGPPs, NPPs, and most ICEVs could all be phased out. Pollution and GHG could be greatly reduced.

Nick Lyons

Are solar cells, electrolizer and FC efficiencies that important when both inputs (sunlight and water) are plentiful and free?

Sunlight is free but diffuse and intermittent. Turning sunlight into electricity is hardly free in any sense of the word.

Potable water is not plentiful everywhere (certainly not here in parched California these days), and it is certainly not free.

Turning diffuse, intermittent wind and solar energy into some kind of usable, stored energy is unlikely to be cheaper than burning abundant coal any time soon, I'm sad to say.

Roger Pham

Electrolysis is 66%-efficient if the H2 is used to produce power, or LHV. If efficiency of FC is 60%, then round trip efficiency is 40%.

Electrolysis is 80%-efficient if the H2 is used for winter heating, or for combined heat and power generation, or HHV. Heat is harvested at almost 100%, so the round-trip efficiency is almost 80%.
This is just as good as any other energy storage means, including battery, which has round-trip efficiency of 80-90%.

So, use battery for short-term electricity storage, and use H2 for seasonal-scale winter heat and power co-generation, in order to phase out fossil fuels.

Roger Pham

@Nick,
The secret in low cost usage of H2 has to do with distributed power and heat co-generation (CHP). With coal or Nat Gas for power, 2/3 to 1/2 of the energy is lost as waste heat at the power plant.

Soon, RE will cost as little as 2-3 cents/kWh. This is comparable to the thermal cost of NG at $6-9/MMBTU, so cost competitive with NG for heating. NG for electricity will cost 2-3x this much due to loss in waste heat and investment in CCGT power plant. Future H2 from low-cost RE, for CHP, will cost 1/2 as much as NG as well as coal for power generation.

As Aha

so for H2 you use cogeneration, but NG and coal figures are without...
Oh and it would be nice district heating system relying on heat from h2o splitting from wind energy...

ai_vin

Sunlight is free but diffuse and intermittent. Turning sunlight into electricity is hardly free in any sense of the word.

The energy payback time for solar cells is .5-1.5 years. As the systems can last 20-30 years...then yes, turning sunlight into electricity is mostly free.

Nick Lyons

The energy payback time for solar cells is .5-1.5 years. As the systems can last 20-30 years...then yes, turning sunlight into electricity is mostly free.

Soon, RE will cost as little as 2-3 cents/kWh.

Without subsidies? Can you provide links?

ai_vin

What about the subsidies the fossil fuel industries get? By comparison RE subsidies are a drop in the bucket.

ai_vin

so for H2 you use cogeneration, but NG and coal figures are without...
Oh and it would be nice district heating system relying on heat from h2o splitting from wind energy...

Good point. And yes district heating is a great idea & should be used wherever possible, but the thing about electrolizer and FC units is they can be made small enough to fit in your house so any waste heat can be used directly.

ai_vin

ADD: With coal or Nat Gas power plants OTOH people prefer they be a good distance away from population centers so a lot potential for waste heat use is lost.

HarveyD

The added (huge) cost of pollution from fossil fues.

A very recent university study confirmed the link between increased pollution from fossil fuel burning and very serious incurable brain diseases.

Treatment and lack of productivity cost over 15 years is very high and not always accounted for.

Bernard

Sunlight is not free in large quantities. The cost of sunlight is the cost of real estate.

HarveyD

Real estate to transform Coal, NG, Oil, bio-mass and radio active materials into electricity is also very costly, specially when total environmental and health cost are duly and fully considered.

They also receive large direct and indirect subsidies.

Smaller combined units could eventually capture solar and/or wind energy and transform it into electricity and stored H2 + heat and visa-versa, to satisfy the need for small-large condo buildings, offices, hotels, motels, schools, hospitals, shopping centers etc.

Roger Pham

@Bernard,
If new buildings and houses are designed with solar PV panels and are prewired, no real estate cost and very low installation cost. Cost of PV modules is on the way to 50 cents per watt, so with preinstalled, total cost will be on order of $1/W. This will result in 2-3 cents/kWh and competitive with Nat Gas cost.

SJC

Electrolysis is endothermic, it requires heat input. Much of the heat created due to loses is used in the electrolysis process. Stop saying you are going to use the waste heat from a PEM electrolyzer.

http://en.wikipedia.org/wiki/Polymer_electrolyte_membrane_electrolysis

ai_vin

Another no-extra-real-estate idea for solar power is covered parking lots. Using solar panels as the rooftop of a carpark can not only generate electricity but also block sunlight from the vehicles to keep their insides cool.

SJC

You can use the heat from a PEM fuel cell, 60% efficient electrolysis and 50% efficient fuel cell is still a THIRTY percent efficient storage, device by the time you compress the hydrogen.

It might be nice to think of a Jetson's home of the future with a fuel cell, but solar panels and a battery bank makes more sense.

HarveyD

Battery banks may be OK for short periods but stored H2 may be better for longer rainy days and winter days?

SJC

I would not want compressed hydrogen at my home for extended periods. Buy a used LEAF pack, if that is not enough, buy two, three or four. If four days storage is not enough, use the grid. It would be cheaper than an electrolyzer, compressor, tank and fuel cell. Besides, you are just venting oxygen with an electrolyzer.

Bernard

It seems that everybody's example of "no-extra-cost" includes significant extra costs.

I maintain that sunny real estate that is near large sources of potable water is a limited, and thus high-cost, resource.

Davemart

SJC:
Norsk Hydro hit up to 80% electrolysis efficiency (HHV) so why are you using 50%?

'Norsk Hydro Electrolysers (NHE) is today a leading
producer of alkaline electrolysers. Some of NHE’s
electrolysers have an efficiency of over 80% (high heating
value'

http://www.bellona.org/filearchive/fil_Hydrogen_6-2002.pdf

In the other direction in the home or office waste heat can certainly be used for how water, so the overall efficiency both ways is around 0.8*0.8 = 64%

(page 20)

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