Making Fuel Cells for a Fraction of the Cost

It is the third announcement in less than one week for a major improvment in the making of fuel cells.

In the competition between Lithium-Ion batteries (e.g. Tesla cars), and hydrogen fuel cells (see picture of Nexo from Hyundai) that power electric cars, it is difficult to predict which one will be the winner at the end.

Fuel cells have the potential to be a clean and efficient way to run cars, computers, and power stations, but the cost of producing them is limiting their use. That’s because a key component of the most common fuel cells is a catalyst made from the precious metal platinum.

In a paper published in Small, researchers at the University of California, Riverside (UCR), describe the development of an inexpensive, efficient catalyst material for a type of fuel cell called a polymer electrolyte membrane fuel cell (PEMFC), which turns the chemical energy of hydrogen into electricity and is among the most promising fuel cell types to power cars and electronics.

The catalyst developed at UCR is made of porous carbon nanofibers embedded with a compound made from a relatively abundant metal such as cobalt, which is more than 100 times less expensive than platinum. The research was led by David Kisailus, the Winston Chung Endowed Professor in Energy Innovation in UCR’s Marlan and Rosemary Bourns College of Engineering.

Fuel cells, which are already being used by some carmakers, offer advantages over conventional combustion technologies, including higher efficiency, quieter operation and lower emissions. Hydrogen fuel cells emit only water.

Like batteries, fuel cells are electrochemical devices that comprise a positive and negative electrode sandwiching an electrolyte. When a hydrogen fuel is injected onto the anode, a catalyst separates the hydrogen molecules into positively charged particles called protons and negatively charged particles called electrons. The electrons are directed through an external circuit, where they do useful work, such as powering an electric motor, before rejoining the positively charged hydrogen ions and oxygen to form water.

A critical barrier to fuel cell adoption is the cost of platinum, making the development of alternative catalyst materials a key driver for their mass implementation.

Using a technique called electrospinning, the UCR researchers made paper-thin sheets of carbon nanofibers that contained metal ions — either cobalt, iron or nickel. Kisailus and his team, collaborating with scientists at Stanford University, determined that the new materials performed as good as the industry standard platinum-carbon systems, but at a fraction of the cost. “The key to the high performance of the materials we created is the combination of the chemistry and fiber processing conditions,” Kisailus said


Electronics: How To Dissipate Heat in A Nanocomputer

Controlling the flow of heat through semiconductor materials is an important challenge in developing smaller and faster computer chips, high-performance solar panels, and better lasers and biomedical devices. For the first time, an international team of scientists led by a researcher at the University of California, Riverside has modified the energy spectrum of acoustic phononselemental excitations, also referred to as quasi-particles, that spread heat through crystalline materials like a wave—by confining them to nanometer-scale semiconductor structures. The results have important implications in the thermal management of electronic devices. Led by Alexander Balandin, Professor of Electrical and Computing Engineering and UC Presidential Chair Professor in UCR’s Bourns College of Engineering, the research is described in a paper published in the journal Nature Communications.


The team used semiconductor nanowires from Gallium Arsenide (GaAs), synthesized by researchers in Finland, and an imaging technique called Brillouin-Mandelstam light scattering spectroscopy (BMS) to study the movement of phonons through the crystalline nanostructures. By changing the size and the shape of the GaAs nanostructures, the researchers were able to alter the energy spectrum, or dispersion, of acoustic phonons. The BMS instrument used for this study was built at UCR’s Phonon Optimized Engineered Materials (POEM) Center, which is directed by Balandin.

Controlling phonon dispersion is crucial for improving heat removal from nanoscale electronic devices, which has become the major roadblock in allowing engineers to continue to reduce their size. It can also be used to improve the efficiency of thermoelectric energy generation, Balandin said. In that case, decreasing thermal conductivity by phonons is beneficial for thermoelectric devices that generate energy by applying a temperature gradient to semiconductors.

For years, the only envisioned method of changing the thermal conductivity of nanostructures was via acoustic phonon scattering with nanostructure boundaries and interfaces. We demonstrated experimentally that by spatially confining acoustic phonons in nanowires one can change their velocity, and the way they interact with electrons, magnons, and how they carry heat. Our work creates new opportunities for tuning thermal and electronic properties of semiconductor materials,” Balandin said.


How To Make Solar Energy Conversion More Efficient

When it comes to installing solar cells, labor cost and the cost of the land to house them constitute the bulk of the expense.  The solar cells – made often of silicon or cadmium telluride – rarely cost more than 20 percent of the total costSolar energy could be made cheaper if less land had to be purchased to accommodate solar panels, best achieved if each solar cell could be coaxed to generate more power.

A huge gain in this direction has now been made by a team of chemists at the University of California, Riverside (UCR) that has found an ingenious way to make solar energy conversion more efficientThe researchers report in Nano Letters that by combining inorganic semiconductor nanocrystals with organic molecules, they have succeeded in “upconvertingphotons in the visible and near-infrared regions of the solar spectrum.


Solar-panels UCRChemists at the University of California, Riverside have found an ingenious way to make solar energy conversion more efficient

The infrared region of the solar spectrum passes right through the photovoltaic materials that make up today’s solar cells,” explained Christopher Bardeen, a professor of chemistry. The research was a collaborative effort between him and Ming Lee Tang, an assistant professor of chemistry. “This is energy lost, no matter how good your solar cell.  The hybrid material we have come up with first captures two infrared photons that would normally pass right through a solar cell without being converted to electricity, then adds their energies together to make one higher energy photon.  This upconverted photon is readily absorbed by photovoltaic cells, generating electricity from light that normally would be wasted.”


How To Boost Electric Vehicle Batteries

Researchers from the Professor Mihri Ozkan lab at the University of California, Riverside’s Bourns College of Engineering have developed a novel paper-like material for lithium-ion batteries. It has the potential to boost by several times the specific energy, or amount of energy that can be delivered per unit weight of the battery.
This paper-like material is composed of sponge-like silicon nanofibers more than 100 times thinner than human hair. It could be used in batteries for electric vehicles and personal electronics.

electric carThe problem with silicon is that is suffers from significant volume expansion, which can quickly degrade the battery. The silicon nanofiber structure created in the Ozkan’s labs circumvents this issue and allows the battery to be cycled hundreds of times without significant degradation. This technology also solves a problem that has plagued free-standing, or binderless, electrodes for years: scalability. Free-standing materials grown using chemical vapor deposition, such as carbon nanotubes or silicon nanowires, can only be produced in very small quantities (micrograms). However, the team was able to produce several grams of silicon nanofibers at a time even at the lab scale.

The nanofibers were produced using a technique known as electrospinning, whereby 20,000 to 40,000 volts are applied between a rotating drum and a nozzle, which emits a solution composed mainly of tetraethyl orthosilicate (TEOS), a chemical compound frequently used in the semiconductor industry. The nanofibers are then exposed to magnesium vapor to produce the sponge-like silicon fiber structure.

The findings were just published in the journal Nature Scientific Reports.

How To Build A Nanocomputer Using Graphene

A team of researchers from the University of California, Riverside’s Bourns College of Engineering, led by Alexander Balandin and Roger Lake, have greatly facilitate the use of graphene in electronic devices. A transistor implemented with graphene will be very fast but will suffer from leakage currents and power dissipation while in the off state because of the absence of the energy band gap. Efforts to induce a band-gap in graphene via quantum confinement or surface functionalization have not resulted in a breakthrough. Now, thanks to the University of California Riverside team findings, graphene applications in electronic circuits for information processing are feasible.

Graphene is a single-atom thick carbon crystal with unique properties beneficial for electronics including extremely high electron mobility and phonon thermal conductivity. However, graphene does not have an energy band gap, which is a specific property of semiconductor materials that separate electrons from holes and allows a transistor implemented with a given material to be completely switched off

Most researchers have tried to change graphene to make it more like conventional semiconductors for applications in logic circuits,” Balandin said. “This usually results in degradation of graphene properties. For example, attempts to induce an energy band gap commonly result in decreasing electron mobility while still not leading to sufficiently large band gap.
We decided to take alternative approach,” Balandin said. “Instead of trying to change graphene, we changed the way the information is processed in the circuits.”