Low carbon process improves hydrogen yields from coal and biomass

While the cleanest hydrogen is produced from renewables, and the majority from natural gas, there remains industrial demand for cheap hydrogen from cheap sources. Coal or biomass solid fuel reactors can be used to cheaply produce hydrogen, but the low yield and carbon emissions have hitherto made this an unattractive long-term solution.

However, researchers from the University of Edinburgh and Yonsei University (South Korea) have now found a way to produce higher yields of ultra-pure hydrogen from solid feedstock. Dr Hyungwoong Ahn, a Senior Lecturer in Chemical Engineering from the University of Edinburgh’s School of Engineering, explains:

“By integrating a coal‐to‐hydrogen process with carbon capture, the hydrogen yield per unit coal feed can be greatly improved using the carbon capture unit on a synthesis gas stream generated by coal gasification. This helps to improve the hydrogen yield by greater and more efficient use of the H2 Pressure Swing Absorption (PSA) tail gas – an important separation process for gases and applied widely in gas purification and gas recovery.”

The researchers claim that their method increases yields by 2%. Furthermore, by using the byproduct waste gas to fuel a carbon capture unit, the system is cleaner than it would otherwise be, if still a long way from carbon neutral.

The University of Edinburgh is excited by the new process, and their Research and Innovation arm is looking to partner with industry to license the technology. Anybody interested in finding out more about the technology with a view to a collaborative research or license agreement should click through here to find out more.

A feasibility study of storing hydrogen in depleted gas reservoirs

If a full scale hydrogen economy is to become a reality, we are going to be producing a lot of hard-to-store fuel. One of the advantages of hydrogen as a resource is that it can be produced during times of surplus renewable energy and stored for a rainy day. However, for this cycle to prove reliable on a national scale, we will need to find ways to store excess hydrogen – possibly for many months.

A. Amid, D. Mignard and M. Wilkinson from the University of Edinburgh have just published a study in the International Journal of Hydrogen Energy, looking into the possibility of using depleted natural gas reservoirs for pressurised hydrogen storage. As of January 2013, a total of 688 natural gas storage facilities were operated worldwide with a combined working gas capacity of 377 billion m3, so if it proved technically feasible there would certainly be scope to take advantage of these spaces.

The researchers’ analysis foresaw three technical problems. First, that the remnant methane in reservoirs would contaminate the hydrogen. Second, that micro-organisms could feed on the hydrogen while it is in storage; and third, that the hydrogen will leak from its prison.

The team’s modelling was based on a partially depleted natural gas reservoir in the Southern North Sea, off the coast of Yorkshire. Their findings were,

  • Contamination: That initial injection cycles could see some methane contamination, but this was ‘not a serious concern’, and the contaminants would be cleansed over multiple cycles. Hydrogen sulphide could prove an issue, and reservoirs should be chosen to minimise the amount of sulphate reducing bacteria.
  • Consumption: There would be some loss of hydrogen as it is converted to methane and biomass, but the worst case scenario would put this at no more than 3.7% of the hydrogen.
  • Leakage: Hydrogen is more diffuse than methane, and so we could expect some leakage, but it is unlikely to be more than 0.035% of the stored hydrogen after 12 months.

In conclusion, the assessment found that there is no insurmountable technical barrier to this plan, given current technology. However it would be a major undertaking, with an average power in the order of 4–5 GW required during a six month injection cycle to fill the reservoir to capacity, provided that cushion gas is already present.

To read the study in full, click through to the International Journal of Hydrogen Energy, Volume 41, Issue 12, 6 April 2016, Pages 5549–5558.

 

EasyJet to trial hybrid fuel-cell systems for air fleet

Source: Arstechnica

British low-cost airline EasyJet has announced its plan to cut fuel costs and carbon emissions by turning to hydrogen fuel cell technology. This doesn’t mean they’re about to fly on hydrogen power – we’re not quite there yet – but EasyJet believes it can use hydrogen fuel cells to power aircraft’s taxiing to and from runways.

EasyJet’s initial press release was a little unclear on technical details, and many of the media reports seem to have conflated fuel cell and battery technology. It seems that the airline plans to install a hydrogen fuel cell in the hold, replacing the traditional auxiliary power unit. This will be a backup to a battery system that will regain charge from photovoltaics in the plane roof, as well as a kinetic energy recovery system connected to the landing gear. The latter technology captures energy that would otherwise be lost during braking, and draws on advances made in the racing car industry over recent years.

Taxiing makes up 4% of EasyJet’s total fuel expenditure, so this melange of energy storage could make for significant carbon savings. Ian Davies, the airline’s Head of Engineering, said that the concepts grew from work done with Cranfield University to envision what the airplanes of 2030 might look like.

Initial public response has been muted, with tabloids seizing on the possibility that passengers might be forced to drink ‘waste’ water produced as a byproduct of the hydrogen process. Nonetheless, EasyJet presses on, and hopes to trial the system later this year.

Hydrogen takes to the sky

Aerial drones have already changed the face of warfare and become a favoured toy for the technorati. Now they look set to shake up commercial delivery systems as well, with Google and Amazon prepping competing drone delivery systems for launch over the next eighteen months.

Drones are still held back, however, by their power sources. The high energy demand of keeping a robot in the air means that range and flight time of commercial drones is quite limited. Sensing an opening, Intelligent Energy has developed a hydrogen fuel cell aimed squarely at the drone market. The company claims that their cell can extend airtime from the current 30 minutes or so, to several hours. It would also allow for a much quicker refueling system than would be possible with traditional batteries.

The claims have yet to be tested on an industrial scale, but Intelligent has issued a press release announcing a partnership with a ‘major drone manufacturer.

Hydrogen’s biggest commercial barrier is the inertia in existing transportation systems. To see mass adoption of hydrogen cars will require a vast program of refitting petroleum stations to utilise a new technology. Drones, though, are a new frontier, and the infrastructure is still being built. This may give hydrogen a real chance to shine against its competitors – if the technology can fulfill its potential.

A model for an integrated wind+hydrogen network for the UK

For all the strides being made in hydrogen fuel cell transportation, we are still a long, long way from having hydrogen form a central pillar in our energy infrastructure. What would the UK look like with a hydrogen based transport sector? Is it even possible, let alone feasible?

To try and answer that question, a partnership between engineering and business researchers at Imperial College have produced a 30 page analysis entitled ‘Optimal design and operation of integrated wind-hydrogen-electricity networks for decarbonising the domestic transport sector in Great Britain’, published in this month’s International Journal of Hydrogen Energy.

The ambitious model hypothesised a closed-loop hydrogen sector, where the UK’s fuel cell vehicle fleet is powered by hydrogen produced by wind power. The modellers converted all UK petrol demand into equivalent hydrogen demand, based on average fuel economies of current petrol and fuel cell cars. To meet that demand, they then sought to determine the optimal number, size and location of wind turbines, electrolysers, hydrogen storage, fuel cells, compressors and expanders. Their conclusion,

Results indicate that all of Britain’s domestic transport demand can be met by on-shore wind through appropriately designed and operated hydrogen-electricity networks. Within the set of technologies considered, the optimal solution is: to build a hydrogen pipeline network in the south of England and Wales; to supply the Midlands and Greater London with hydrogen from the pipeline network alone; to use Humbly Grove underground storage for seasonal storage and pressurised vessels at different locations for hourly balancing as well as seasonal storage; for Northern Wales, Northern England and Scotland to be self-sufficient, generating and storing all of the hydrogen locally. These results may change with the inclusion of more technologies, such as electricity storage and electric vehicles.

Optimal distribution network for hydrogen economy.
Fig 1: Optimal distribution network for hydrogen economy (http://www.sciencedirect.com/science/article/pii/S0360319915300574)

The envisioned pipeline, indicated by the red line across the south of England in the figure above, would be needed to supply the UK’s southern urban centres.

How much would all this cost? The modellers have suggested £17.1 bn/yr once the infrastructure is up and running, itself budgeted at £4.7 billion. This includes the use of large, underground reservoirs to store hydrogen in winter, when demand is lowest, and release it out during the summer months. Without storage reservoirs, the estimated cost of the network rises by 25% to meet peak demand.

Such a radical overhaul of the UKs transport and energy sectors is unlikely in the short term, to say the least, but such concrete proposals give policymakers a starting point to consider the matter more seriously. To see the full list of assumptions, calculations and conclusions in the model, you can read the full paper at the International Journal of Hydrogen Energy here.

Nickel-based catalyst performs competitively with platinum in hydroxide exchange membrane fuel cells

The hunt for platinum’s successor as a hydrogen oxidation catalyst continues in this month’s Nature Communications (Zhuang, Z. et al. Nickel supported on nitrogen-doped carbon nanotubes as hydrogen oxidation reaction catalyst in alkaline electrolyte. Nat. Commun. 7:10141 doi: 10.1038/ncomms10141 (2016)).

A research team from the University of Delaware, in partnership with Beijing University of Chemical Technology, have made a breakthrough in their search for a low-cost catalytic material. After switching from an acidic to an alkaline environment, the researchers experimented with nickel nanoparticles supported on nitrogen-doped carbon nanotubes. According to their results, this composite catalyst can produce a hydrogen oxidation activity comparable to platinum-group metals in alkaline electrolyte. In their words,

Although nitrogen-doped carbon nanotubes are a very poor hydrogen oxidation catalyst, as a support, it increases the catalytic performance of nickel nanoparticles by a factor of 33 (mass activity) or 21 (exchange current density) relative to unsupported nickel nanoparticles. Density functional theory calculations indicate that the nitrogen-doped support stabilizes the nanoparticle against reconstruction, while nitrogen located at the edge of the nanoparticle tunes local adsorption sites by affecting the d-orbitals of nickel. Owing to its high activity and low cost, our catalyst shows significant potential for use in low-cost, high-performance fuel cells.

The team’s results suggest that when the nitrogen dopants sit at the edge of the nickel nanoparticles, it stabilises and activates the nickel. By multiplying the catalytic effect of the nickel, the nitrogen-doped nanotubes thus bring the cost of the catalyst down to competitive levels.

Finding a cheap alternative catalyst to platinum is one of the necessary steps in scaling up a full-scale hydrogen economy. In a press release, contributing author Yushan Yan expressed his hope that his team’s results would be a step towards that goal,

Our real hope is that we can put hydroxide exchange membrane fuel cells into cars and make them truly affordable — maybe $23,000 for a Toyota Mirai. Once the cars themselves are more affordable, that will drive development of the infrastructure to support the hydrogen economy.

ITM Power and CEME to build East London refuelling station

Fuel cell company ITM Power has signed a memorandum of understanding with The Centre for Engineering and Manufacturing Excellence (CEME) to build a hydrogen refuelling station at CEME’s East London campus.

The groups aim to produce something more than just a place to top up. The plans for the site would make it the de facto London hub for fuel cell electric vehicles, as it will include a fuel cell vehicle maintenence and training centre, a research institute and the headquarters for ITM Power’s London maintenance team.  There is no word yet on the timetable.

 

Berkeley Lab funded for hydrogen storage research

Berkeley Lab in California has just been awarded $8 million from the US Department of Energy for two of their projects: one to find new materials for hydrogen storage and another for optimizing fuel-cell performance and durability. The grant, from the Fuel Cell Technologies Office, shows that the American government is taking hydrogen as a serious contender alongside other next-generation energy technologies.

Jeff Urban, the HyMARC lead scientist for Berkeley Lab, said: “Berkeley Lab brings to the consortium a combination of innovation in H2 storage materials, surface and interface science, controlled nanoscale synthesis, world-class user facilities for characterizing nanoscale materials, and predictive materials genome capabilities.”

Cobalt catalyst outperforms metal-free competitors

The race to find a substitute to platinum as a fuel-cell catalyst continues, with cobalt the latest alternative to be put forth. In a Nature Communications article from last week, a Chinese-American team reported successful results by attaching a small number of cobalt atoms to nitrogen pre-embedded in a graphene substrate.

Here, we report an inexpensive, concise and scalable method to disperse the earth-abundant metal, cobalt, onto nitrogen-doped graphene (denoted as Co-NG) by simply heat-treating graphene oxide (GO) and small amounts of cobalt salts in a gaseous NH3 atmosphere. These small amounts of cobalt atoms, coordinated to nitrogen atoms on the graphene, can work as extraordinary catalysts towards HER in both acidic and basic water.

Control tests with nitrogen enhanced graphene on its own showed very little catalytic power, but the inclusion of a dusting of cobalt atoms produced a material comparable to platinum-carbon in its onset voltage (30mV). Stress tests showed little degradation in activity over ten hours.

In the eyes of team member James Tour, from Rice University, what makes the research groundbreaking is that it is predicated on the manipulation of single atoms, rather than particles or nanoparticles. He explained, “in our process the atoms driving catalysis have no metal atoms next to them. We’re getting away with very little cobalt to make a catalyst that nearly matches the best platinum catalysts.

Using cobalt, the researchers claim that they were able to achieve a superior hydrogen evolution reaction to that seen in any comparable metal-free catalysts, including MoS2 (see Supplementary Table 1 here). The team especially stressed the superiority of Co-NG in alkaline media, contrasting it to MoS2 and metal phosphides, which are highly active in acid, but with poor stability and limited application in alkaline electrolysis.

Given its strong stability, Co-NG is mixed as a solution that can then be formed into a ‘paper’ that could be used as a free-standing electrode, or coated onto other conductive substrates. More generally, the research points the way towards new methods of preparing extremely efficient single-atom catalysts that may hold promise as next-generation materials.

To read more, you can see the Rice University’s press release here, and access the paper at Nature Communications.

Substitute catalyst may obsolete platinum

Sandia researcher
Sandia researcher Stan Chou. Source: Randy Montoya

As outlined in Monday’s news, platinum is a world-class catalyst but remains a cost hurdle for fuel cell production. Now, in research outlined in Nature Communications, Sandia National Laboratory scientists have moved away from platinum as a catalyst entirely, turning instead to a cheaper substitute. Molybdenum disulphide, MoS2 or ‘molly’ for short, an inorganic compound similar to graphite, and currently available at less than a hundredth of the price of platinum.

In laboratory conditions MoS2 has been shown to provide a catalytic efficiency approaching platinum’s, but only at the edge of its 2d crystal nanostructure. The interior of the MoS2, which makes up the vast majority of a given sample, is differently structured and unreactive with hydrogen. As a catalyst therefore, MoS2 was 90% dead weight.

However, by using lithium to ‘pull apart’ the sheets of a MoS2 lattice, the Sandia team were able to increase the material’s surface area and, more importantly, produce a change in structure that activated the catalytic properties of the interior.

To a degree, this upgrade effect has been recognised since 1973, but the mechanisms involved were poorly understood and difficult to replicate. The Sandia team’s advance is to map exactly how and why the improved catalyst works, and thus pave the way for using MoS2 in industrial hydrogen production.

“It’s photosynthesis, but using inorganic materials rather than plants,” lead author Stan Chou explained. “Plants use enzymes powered by sunlight to break up water into hydrogen and oxygen in a delicate process. We’re proposing a similar thing here, but in a more rapid reaction and with sturdier components.”

The team claims that their upgraded Molly has already increased the yield of hydrogen production by over four times. If replicated, their model could see a big price drop in fuel cell costs going forward.

Source: Nature Communications 6, Article number: 8311 (free to public)