One potential clean energy future requires an economical, efficient, and relatively simple way to generate copious amounts of hydrogen for use in fuel-cells and hydrogen-powered vehicles. 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 have discovered a way to make great improvements, giving hope to using two of the most abundant elements on earth to efficiently produce hydrogen.
Hematite holds potential for use in low-power photoelectrochemical water splitting (where energy, in the 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 volts when exposed to sunlight. Unfortunately, that voltage is too low to initiate water-splitting so a number of improvements to the surface of hematite have been sought to improve current flow.
In this vein, researchers from Boston College, UC Berkeley, and China's University of Science and Technology have hit upon the technique of "re-growing" the hematite, so that a smoother surface is obtained along with a higher energy yield. In fact, this new version has doubled the electrical output, and moved one step closer to enabling practical, large-scale energy-harvesting and hydrogen generation.
"By simply smoothing the surface characteristics of hematite, this close cousin of rust can be improved to couple with silicon, which is derived from sand, to achieve complete water splitting for solar hydrogen generation," said BostonCollege associate professor of chemistry Dunwei Wang. "This unassisted water splitting, which is very rare, does not require expensive or scarce resources."
Working on previous work that realized gains in the photoelectrochemical turn-on voltage from the use of smooth surface coatings, the team re-assessed the hematite surface structure by employing a synchrotron particle accelerator at the Lawrence Berkeley National Laboratory. Concentrating on massaging the hematite's surface deficiencies to see if this would result in improvements, the researchers used physical vapor deposition to layer hematite onto a borosilicate glass substrate and create a photoanode. They then baked the devices to produce a thin, even film of iron oxide across their surfaces.
Subsequent tests of this new amalgam resulted in an immediate improvement in turn-on voltage, and a substantial increase in photovoltage from 0.24 volts to 0.80 volts. Whilst this new hydrogen harvesting process only realized an efficiency of 0.91 percent, it is the very first time that the combination of hematite and amorphous silicon has been shown to produce any meaningful efficiencies of conversion at all.
As a result, this research has shown that progress has been made towards the possibility of producing photoelectrochemical energy harvesting that is totally self-sufficient, uses abundantly available materials, and is easy to produce.
"This offers new hope that efficient and inexpensive solar fuel production by readily available natural resources is within reach," said Wang. "Getting there will contribute 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
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.
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.
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.
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.
"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 ...
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.