Energy

Solar-powered hydrogen generation using two of the most abundant elements on Earth

By smoothing the surface of hematite, a team of researchers achieved "unassisted" water splitting using the abundant rust-like mineral hermatite and silicon to capture and store solar energy within hydrogen gas
By smoothing the surface of hematite, a team of researchers achieved "unassisted" water splitting using the abundant rust-like mineral hermatite and silicon to capture and store solar energy within hydrogen gas
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By smoothing the surface of hematite, a team of researchers achieved "unassisted" water splitting using the abundant rust-like mineral hermatite and silicon to capture and store solar energy within hydrogen gas
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By smoothing the surface of hematite, a team of researchers achieved "unassisted" water splitting using the abundant rust-like mineral hermatite and silicon to capture and store solar energy within hydrogen gas

One potential clean energy future requires an economical, efficient, and relativelysimple way to generate copious amounts of hydrogen for use in fuel-cells and hydrogen-poweredvehicles. Often achieved by using electricity to split water molecules into hydrogen and oxygen, the ideal method would be to mine hydrogen from water using electricity generated directly from sunlight without the addition of any external power source.Hematite – the mineral form of iron – used in conjunction with silicon has shown some promise in this area,but low conversion efficiencies have slowed research. Now scientists havediscovered a way to make great improvements, giving hope to using twoof the most abundant elements on earth to efficiently produce hydrogen.

Hematite holds potential for use in low-powerphotoelectrochemical water splitting (where energy, inthe form of light, is the input and chemical energy is the output) to release hydrogen due to its low turn-on voltage of less than 0.3 voltswhen exposed to sunlight. Unfortunately, that voltage is too low to initiatewater-splitting so anumber of improvements to the surface of hematite have been sought to improve currentflow.

In this vein, researchersfrom Boston College, UC Berkeley, and China's University of Science andTechnology have hit upon the technique of "re-growing" the hematite, so that asmoother surface is obtained along with a higher energy yield. In fact, thisnew version has doubled the electrical output, and moved one step closer toenabling practical, large-scale energy-harvesting and hydrogen generation.

"Bysimply smoothing the surface characteristics of hematite, this close cousin ofrust can be improved to couple with silicon, which is derived from sand, toachieve complete water splitting for solar hydrogen generation," said BostonCollege associate professor of chemistry Dunwei Wang. "This unassisted watersplitting, which is very rare, does not require expensive or scarce resources."

Workingon previous work that realized gains in the photoelectrochemical turn-onvoltage from the use of smooth surface coatings, the team re-assessed thehematite surface structure by employing a synchrotron particle accelerator atthe Lawrence Berkeley National Laboratory. Concentrating on massaging the hematite'ssurface deficiencies to see if this would result in improvements, theresearchers used physical vapor deposition to layer hematite onto a borosilicateglass substrate and create a photoanode. They then baked the devices to produce athin, even film of iron oxide across their surfaces.

Subsequenttests of this new amalgam resulted in an immediate improvement in turn-onvoltage, and a substantial increase in photovoltage from 0.24 volts to 0.80volts. Whilst this new hydrogen harvesting process only realized an efficiency of0.91 percent, it is the very first time that the combination of hematite andamorphous silicon has been shown to produce any meaningful efficiencies ofconversion at all.

As aresult, this research has shown that progress has been made towards thepossibility of producing photoelectrochemicalenergy harvesting that is totally self-sufficient, uses abundantly availablematerials, and is easy to produce.

"Thisoffers new hope that efficient and inexpensive solar fuel production by readilyavailable natural resources is within reach," said Wang. "Getting there willcontribute to a sustainable future powered by renewable energy."

The results of this research were recently published in the journal Angewandte Chemie International Edition

Source: Boston College via EurekAlert

12 comments
PeterMortensene7877c8e180f4d2a
0.91 percent of efficiency is of course better than 0 percent, but it's very far from anything usable. Efficiency is what matters in the end. One problem with hydrogen is that even you have made it, you still need to compress it, transport it and when you finally convert it into usable energy, you lose a lot of energy too. Just to put things in perspective, the energy equivalent of one gallon of gas is about 10,000 liters of hydrogen at atmospheric pressure. Burning hydrogen in a combustion engine is tremendously inefficient thus you need to use a fuel cell to make electricity out of it. As wonderful as it sounds, poor end-to-end efficiency is the major reason why hydrogen is hard to turn into meaningful use. Solar panels generate electricity directly and already provides enough efficiency to make economical sense also.
martinkopplow
While Peter Mortensen is undoubtedly right that 0,91% efficiency is very little, we must reconsider our view towards efficiency when we talk renewables. Efficiency is very critical as long as limited resources are used, though it becomes less important as soon as the input is abundant, such as solar radiation. I such cases, we might prefer a clean process that has lower efficiency but runs forever over a more efficient process that uses up limited resources, causes pollution and can only run so long. With that in mind, comparing everything to the enery equivalent of gasoline might not be the way to go. Still, the method described here will need to be improved quite some before it can be put to practical use.
Synchro
Comparing to hydrogen at atmospheric pressure is pointless since that's not how you would use it. Like Martin said, the efficiency doesn't matter much if the resources are cheap, abundant and safe (sand and rust!). If you look only at conversion efficiency, we should use only the very best solar panels. But that may prove uneconomic at scale - we need to look at cost per W. The very best panels deliver around 40% efficiency - this technology may deliver 1/40th of the power, but at perhaps 1/1000th the cost, meaning it may still come out well ahead. Petrol is expensive and dangerous to find, extract, transport and use, and solar panels are often limited by space (e.g. the size of your roof), thus requiring more-efficient but expensive panels. But there are places where space constraints do not apply and inefficient (but very cheap) conversion is viable. Your point about transporting hydrogen is correct, but it's essentially the same as for petrol. I suspect a big, cheap hydrogen solar plant in a desert feeding local storage and giant fuel cells might make a reasonable stored power resource where things like pumped hydro is not viable.
Fretting Freddy the Ferret pressing the Fret
Agreed with Peter. This conversion efficiency is still very far away from considering scaling it up. A finer point is that turning input energy (photons) into chemical energy, and then turning it back into electricity is unfavourable when compared to solar cells. With solar cells, input energy is directly converted to electricity. The extra step in converting chemical energy back into electricity (about 60% efficiency in fuels cells) means that a significant amount of energy is lost this way. You have to have as few as possible energy conversion steps from one form to another from (chemical, electrical, thermal, ...) to minimise losses, or else existing alternatives will often make more sense in using.
StevenHall
Have to agree with Fretting Freddy the Ferret pressing the Fret and Peter. "You have to have as few as possible energy conversion steps from one form to another..." "Like Martin said, the efficiency doesn't matter much if the resources are cheap, abundant and safe (sand and rust!)." I disagree !!! Many people in various Industries said that about oil ,food and clean water. Efficiency Does Matter ...
michael_dowling
Probably better to use high efficiency solar cells to charge flow batteries for energy storage as opposed to generating h2o which would be used to run fuel cells.
Don Duncan
Peter: "Solar panels...already provides enough efficiency..."? For what? Not for fueling a vehicle or plane. Battery tech requires storing and the heavy storage device must be carried along, with conversion losses in/out. 100 years from now gas may still be #1. No one can predict. What I can say with certainty is that the worldwide system of energy production is fundamentally flawed. It is crippled by govt. interference. Take govt. out of the picture, and we will always have the most efficient system. Free enterprise works. The current system of some freedom, some politics, is costing lives/money.
Douglas Bennett Rogers
The life cycle energy cost is the crux of the problem. This gives the cost per unit energy. Installed nuclear wins hands down, followed by coal and natural gas. Regulations and lawsuits upset this order. Power to weight ratio makes oil preferred for vehicles. Nuclear has good energy and power to weight ratios so it is used for naval ships and space probes, where political objections can be overcome.
Clarity
Douglas- I guess it depends on what you include in your "life cycle enrgy costs" and all the possible outcomes and effects of each choice.
pmshah
At lab level this may be OK but can it be scaled up ? Pure H2O is non conductive so you would have to acidify it. Just wonder how well this so called "Rust" electrode stand up in such environment?