Prima di parlare di scelte sostenibili da parte dei governi, si calcolano i vantaggi e svantaggi degli interventi.
A livello di ricerca alimentare, le fonti proteiche alternative si sono indirizzate sulle FARMS di insetti. Ma quanto costa un kilo di farina di insetti (grilli, ad esempio)? 70 euro al kilo. Quindi, un pacco di pasta contenente il 10% di farina di insetti dovrebbe costare 7 euro.
A livello di fonti energetiche alternative ai combustibili fossili, si parla a fasi alterne della possibilità di usare l'idrogeno, che bruciando non produce anidride carbonica. Il costo dell'idrogeno per uso automobilistico è elevato (17 euro/litro) e manca l'infrastruttura. Inoltre, per la conversione in energia si usano le celle combustibili, un processo che disperde parte dell'energia, invece di motori che brucino direttamente H2, anche se alcuni modelli di auto sono stati prodotti.
L'idrogeno si produce con metodi ecologici (green) o non ecologici (Blu) partendo dal consumo di energia convenzionale, che aumenta la CO2.
Nessuno fino ad oggi aveva ventilato la fattibilità delle elettrolisi dell'acqua per produrre H2, perchè i catalizzatori usati sono le terre rare come l'iridio.
Oltre all'impiego di idrogeno nelle batterie (fuel cells) con efficenza dell'80%, è stato messo a punto da Toyota un motore a indrogeno, motori prodoti dall'azienda Acquarius, basato su un cilindro in cui i pistoni si muovono tra due capi del motore (vedi anche
post precedente)
Nelle auto elettriche attuali, aplug in, l'alimentazione elettrica viene prodotta a partire da energie non verdi (carbone, biodiesel), quindi non è sostenibile: consumiamo un eccesso di energie tradizionali per alimentare la rete elettrica, quando dovremmo produrre sorgenti di energia pulita. Questo si traduce nella ricerca di fonti di energia alernaive che non producano CO2: nella classificazione dell'idrogeno, H2, se è prodotto a partire da carbone, petrolio o centrali tradizionali, viene chiamato idrogeno blu, mentre dobbiamo puntare su idrogeno verde, produzione in cui le reazioni che permettono l'elettrolisi dell'acqua sono alimentate da energie rinnovabili.
le tecnologie per produrre idrogeno verde hanno bisogno di uno scale up industriale, e di abbassare il costo a valle. Finchè sarà venduto a 17 euro/litro, le auto ad idrogeno per fare un pieno in Italia devono arrivare all'unico distributore presente, nel Trentino, e compiere con quel pieno 350/400 km. In Germania esistono almeno una ventina di distributori.
Oggi, un articolo che presenta la ricerca del Giappone,
RIKEN institute, mostra un nuovo catalizzatore economico che aumenta la produttività dell'elettrolisi di 4000 volte.
Researchers led by Ryuhei Nakamura at the RIKEN Center for Sustainable Resource Science (CSRS) in Japan have improved on their green and sustainable method of extracting hydrogen from water by using a custom-made catalyst for the chemical reaction. Published in Nature Catalysis, the study details how they manipulated the catalyst’s 3D structure, which led to improved stability and an increase in the catalyst’s lifetime by almost 4,000%. The findings impact the ability to achieve a lasting and sustainable hydrogen-based energy economy.
Water electrolysis using proton exchange membranes is a green electrochemical process for splitting water into oxygen and hydrogen. Hydrogen produced this way can then be stored and used at a later time. For example, when combined with a proton exchange membrane (PEM) fuel cell, the stored hydrogen can be used to power an electric car. However, PEM electrolysis still has limitations that prevent widespread industrial uses such as in power plants. In particular, the necessary chemical reactions happen in a highly acidic environment, and the best catalysts for these reactions are extremely rare earth metals, such as iridium. As Nakamura explains, “scaling up PEM electrolysis to the terawatt scale would require 40 years’ worth of iridium, which is certainly impractical and highly unsustainable.
Almost two years ago, Nakamura and his team developed a breakthrough process that allowed acid water electrolysis that did not rely on rare earth metals. By inserting manganese into a cobalt oxide lattice, they created a process that relied only on common and sustainable earth metals. Despite the success, the process was still not as stable as it needs to be in a PEM electrolyzer. Now, they have built on their previous discovery and developed a longer-lasting earth-abundant catalyst.
The new catalyst is a form of manganese oxide (MnO2). The key finding was that reaction stability could be increased over 40 times by altering the catalyst’s lattice structure. Oxygen in the 3D lattice structure of manganese oxide comes in two configurations, planar and pyramidal. The planar version forms stronger bonds with manganese, and the researchers discovered that increasing the amount of planar oxygen in the lattice significantly enhanced catalytic stability.
They tested four different manganese oxides, which varied in the percentage of planar oxygen. When using the version with the highest achievable percentage, 94%, the critical oxygen evolution reaction could be maintained in acid for one month at 1000 mA/cm2. The total amount of charge transferred in this case was 100 times more than anything seen in previous studies.
When tested in a PEM electrolyzer, water electrolysis could be sustained for about 6 weeks at 200 mA/cm2. The total amount of water electrolyzed in this time period, and therefore the amount of hydrogen produced, was 10 times more than has been achieved in the past with other non-rare metal catalysts. “Surprisingly,” says co-first author Shuang Kong, “the improved stability did not come at a cost in activity, which is usually the case. A PEM water electrolyzer that generates hydrogen with an earth-abundant catalyst at a rate of 200 mA/cm2 is highly efficient.”
Industrial applications typically require a stable current density of 1000 mA/cm2 that lasts for several years, rather than a month. Nevertheless, the researchers think that tangible, real-world applications will eventually be possible and contribute to carbon neutrality. “We will continue to modify catalyst structure to increase both current density and catalyst lifetime,” says Nakamura. “In the long-term, our efforts should help achieve the ultimate objective for all stakeholders — to conduct PEM water electrolysis without the use of iridium.”
Kong et al. (2024) Acid-stable manganese oxides for proton exchange membrane water electrolysis.
Nat Catal. doi:10.1038/s41929-023-01091-3
The new manganese oxide catalyst allows this level of production to last for months in a PEM.
Proton exchange membrane (PEM) water electrolyzer using manganese oxide.
A photocatalyst developed by
researchers at Oregon State University could provide a more efficient route to hydrogen production.
Publishing their research in the journal Angewandte Chemie, the researchers say that their photocatalyst is based on a metal organic framework (MOF). The MOF was used to develop a metal oxide heterojunction – a combination of two materials with complementary properties – to make a catalyst that, when exposed to sunlight, could quickly and efficiently split hydrogen from water.
The heterojunction features MOF-derived ruthenium oxide and titanium oxide doped with sulphur and nitrogen. The researchers tested a number of heterojunctions, which they call RTTA, with different amounts of the oxides and found that the lowest ruthenium oxide content exhibited the fastest rate of hydrogen production.
In just one hour, a gram of RTTA-1 was able to produce more than 10,700 micromoles of hydrogen. The team said the process utilized photons—light particles—at an “impressive” rate of 10%, so that for every 100 photons that struck RTTA-1, 10 contributed to hydrogen production.
The researchers said the photocatalyst could enables the high-speed, high-efficiency production of hydrogen, used in fuel cells for cars as well as in the manufacture of many chemicals including ammonia, in the refining of metals and in making plastics.
"The remarkable activity of RTTA-1 is because of the synergistic effects of the metal oxides’ properties and surface properties from the parent MOF that enhance electron transfer," said Kyriakous Stylianou, assistant professor in the Department of Chemistry at Oregon State University College of Science.
"This study highlights the potential of MOF-derived metal oxide heterojunctions as photocatalysts for practical hydrogen production, contributing to the development of sustainable and efficient energy solutions," Stylianou added.
Current catalytic processes for producing hydrogen from water involve electrocatalysis. The sustainability of this route depends on using renewable energy, and to be competitive in the market, the energy must be inexpensive. Producing hydrogen by splitting water through a catalytic process is cleaner than the conventional method of deriving hydrogen from natural gas via a carbon-dioxide-producing process known as methane-steam reforming.
Techniques that can bring down the cost of producing hydrogen by splitting water are therefore welcome.
Presently, methane-steam reforming produces hydrogen at a cost of about $1.50 per kilogram, compared to about $5 a kilogram for green hydrogen.
Stylianou said: "Ruthenium oxide is not cheap, but the amount used in our photocatalyst is minimal. For industrial applications, if a catalyst shows good stability and reproducibility, the cost of this small amount of ruthenium oxide becomes less important."
Boosting Photocatalytic Hydrogen Production by MOF-derived Metal Oxide Heterojunctions with a 10.0% Apparent Quantum Yield
Emmanuel N. Musa, Ankit K. Yadav, Kyle T. Smith, Min Soo Jung, William F. Stickle, Peter Eschbach, Xiulei Ji, Kyriakos Stylianou
First published: 10 July 2024 https://doi.org/10.1002/anie.202405681
