Back in July 2011 we published an exciting little post on MIT’s work with artificial leaves - MITs Artificial Leaf - based on a silicon solar cell.
The leaf consists of a thin, flat, three-layered silicon solar cell with catalysts bonded to both faces of the silicon. Placed in water and exposed to sunlight, silicon absorbs photons of sunlight, generating electrons with enough energy to conduct through the silicon.
The process leaves behind positively charged electron vacancies called “holes” that can also move through the material. The holes migrate to a cobalt-containing catalyst painted on one face of the silicon cell, where they strip electrons from water molecules, breaking them into hydrogen ions (H+), and oxygen atoms. The catalyst then knits pairs of oxygens together to make O2. Meanwhile, the H+ ions migrate to another catalyst on the opposite face of the silicon cell, where they combine with conducting electrons to make molecules of H2. In principle, the H2 can then be stored and either burned or run through a fuel cell to generate electricity.
This is Photocatalytic water splitting, world meet the ARTIFICIAL LEAF!
Professor Daniel Nocera’s work has finally borne fruit. Nocera’s team developed the catalyst three years ago, the first practical artificial leaf has now been developed, and this new technology may help to deliver efficient carbon neutral energy to the world’s poor and developing nations.
Building on their previous research, the researchers at MIT in Boston have created an artificial leaf that, unlike earlier devices is made from inexpensive materials, and employs low-cost engineering and manufacturing processes ::::
Appearing in the journal Accounts of Chemical Research, this latest technology may help to deliver carbon neutral energy to the world’s poor, helping to provide “global society its most direct path to a sustainable energy future”, said Daniel Nocera.
On our big green/blue globe most of the energy we use comes from photosynthesis. Plants store energy from the Sun in the form of chemical bonds, and we exploit that energy when we eat plants, when we eat animals that eat plants, burn wood, or burn the products of the anaerobic decomposition of these organisms in the form of fossil fuels.
Artificial leaves resemble a thin playing card, described by MIT as a “silicon solar cell with different catalytic materials bonded onto its two sides”. Covered with water and placed in sunlight, it splits hydrogen and water, mimicking photosynthesis.
In a real leaf, the hydrogen is then combined with CO2 from the atmosphere to make sugars, cell walls and other organic matter. In the artificial version, scientists use the hydrogen in fuel cells to make electricity or else combine it with CO2 to make fuels such as methanol. This could be used in car engines, much as ethanol biofuels are used today and would provide a carbon-neutral source of power.
Harnessing this power may hold promising implications for renewable technology. The first breakthrough came with the development of the artificial leaf in 2010 by Nocera and his team. Artificial leaves could also fill some of the gaps left by other renewable energy technology. They could be used in arid regions where hydropower is unfeasible, they take up less space than solar panels and don’t require a battery to store energy.
The device produces a gentle electric current in a similar mechanism to the way solar panels collect sunlight. This gentle current then drives a reaction that separates hydrogen and oxygen from water. These gases can then be used as a fuel source or function as a battery.
Until now, production of these devices was restricted by the expense required to make them, needing rare metals such as platinum, iridium and rhodium to function as a catalyst for the reactions.
However, in a new model created by Nocera’s team, a number of improved catalysts have been developed that not only greatly reduce the cost, but also utilise an innovative approach to produce long-term reliability.
To make these devices more widely available, Nocera replaced the platinum catalyst that produces hydrogen gas with a less-expensive nickel-molybdenum-zinc compound. On the other side of the leaf, a cobalt film generates oxygen gas. Nocera notes that all of these materials are abundant on Earth, unlike the rare and expensive platinum, noble metal oxides and semiconducting materials others have used.
“Considering that it is the 6 billion nonlegacy users that are driving the enormous increase in energy demand by midcentury, a research target of delivering solar energy to the poor with discoveries such as the artificial leaf provides global society its most direct path to a sustainable energy future” Nocera says.
Nocera suggests these devices may help the world’s poorest power their homes for next to nothing. “For the non-legacy world, energy has to be super cheap,” he said. “If I could make alternative energy that was cheap enough for you to run in your house – and I can’t – it still wouldn’t be cheap enough for the poor.
The great humanitarian potential for the technology has continued to drive the project to develop a truly carbon neutral technology. In order in accomplish this, Nocera and colleague Matthew Kanan developed a new model using a more affordable – and widely available – nickel-molybdenum-zinc compound as a catalyst for the hydrogen reaction, and a film of cobalt to produce the oxygen.
Wired.com has a post on a similar technology by chemists Richard Masel of Dioxide Materials in Champaign, Illinois, and Paul Kenis of the University of Illinois Urbana-Champaign, report that they’ve come up with a more energy-efficient approach to converting carbon dioxide (CO2) into carbon monoxide (CO), the first step to making a hydrocarbon fuel. Other researchers have worked for decades to devise catalysts and the right reaction conditions to carry out this conversion. But converting CO2 to CO has always required applying large electrical voltages to CO2 to make the change. That excess voltage is an energy loss, meaning it takes far more energy to make the CO than it can store in its chemical bonds, read the full post at www.wired.com
source: accounts of chemical research
source: science daily
related: MITs Artificial Leaf