Team at Australia's RMIT finds silicon contamination of graphene as a hindrance to commercial adoption

Researchers at Royal Melbourne Institute of Technology (RMIT) have found that graphene could better fulfill its potential when purified to remove silicon, doubling its electrical performance.

Despite researchers demonstrating countless possible applications of graphene, many people feel that graphene is thus far showing rather sluggish industrial adoption. Now, researchers based at RMIT have proposed a possible reason for this and suggested how graphene's full potential could be unlocked.

Researchers develop a technique to fabricate large squares of graphene riddled with controlled holes

Researchers at MIT have found a way to directly “pinprick” microscopic holes into graphene as the material is grown in the lab. Using this technique, they have fabricated relatively large sheets of graphene (roughly the size of a postage stamp), with pores that could make filtering certain molecules out of solutions vastly more efficient.

Holes would typically be considered unwanted defects, but the MIT team has found that certain defects in graphene can be an advantage in fields such as dialysis. Typically, much thicker polymer membranes are used in laboratories to filter out specific molecules from solution, such as proteins, amino acids, chemicals, and salts. If it could be tailored with selectively-sized pores that let through certain molecules but not others, graphene could substantially improve separation membrane technology.

Japanese team designs a graphene-based electrode that can produce hydrogen under acidic conditions

Researchers at the Japanese Tsukuba University described a graphene-based electrode that can produce hydrogen under acidic conditions. The electrolysis of water to generate hydrogen is vital for energy storage in a green economy. One of the major obstacles, however, is the high cost of noble-metal electrodes. Cheaper non-noble electrodes function well in driving the hydrogen evolution reaction (HER), but mainly in alkaline conditions, where the reaction is electricity-hungry. The more efficient acid-phase reaction requires precious metals such as platinum. Worse still, the acid electrolytes are corrosive and eat away at the core metal.

Perforated graphene for hydrogen production image

The researchers have found that holey graphene offers a way around this problem. They used nitrogen-doped graphene sheets to encapsulate a nickel–molybdenum (NiMo) electrode alloy. The graphene was punched full of nanometer-size holes. The researchers showed that in acid conditions, their HER system dramatically outperforms an electrode using regular non-holey graphene. The use of graphene in HER electrodes is not new—this flexible, conductive carbon sheet is ideal for wrapping around the core metal. However, although it protects the metal against corrosion, graphene also suppresses its chemical activity. In the Tsukuba system, the holes promote the reaction in two ways, while the intact graphene part protects the metal.

New growth method yields wrinkle-free graphene

A team of researchers from China has designed a new growth method that produces smooth and pristine graphene. Using a carefully engineered substrate, the researchers can grow high-quality graphene free of wrinkles that often form during manufacture. The team reports that the super-smooth graphene has shown improved electrical properties over rumpled graphene grown by the usual methods.

Special substrate yields smoother graphene image

Existing methods usually use copper foil as a growth substrate to form a sheet of graphene. However, the research team hypothesized that a mismatch in material properties between between graphene and the copper growth substrate may be the cause of wrinkling that often damage the resulting graphene's properties. Graphene and the form of copper usually used as substrate expand at different rates at a given temperature, leading to mechanical strain and causing wrinkling. So, the team searched for copper substrates with a crystalline structure that’s a better match.

Two projects demonstrate how metal-oxide coatings influence graphene

Two interesting projects focused on coating single-layer graphene with metal-oxide nanolayers were presented at the latest Thin Films and Coating Technologies for Science and Industry event in the UK. Researchers from Cranfield University, UK, together with collaborators from University of Cambridge and the Centre for Process Innovation (CPI), applied alumina to form a composite barrier layer, while a team from Imperial College London, UK, used the unique properties of strontium titanate to fabricate a tuneable capacitor.

The researchers of the first project explained that in theory, graphene should represent an ideal ultrathin barrier layer, as the pores between carbon atoms are smaller even than the radius of a helium atom. In practice, however, crystal boundaries and missing atoms allow vapor to permeate through the material, and the weak van der Waals bonds between planes mean that even stacks of multiple graphene layers can be penetrated. The solution reported by the team is to take a graphene monolayer formed by CVD, and to then use atomic layer deposition (ALD) to coat it with a 25–50 nm thick layer of alumina. Achieving conformal coatings on single-layer graphene is known to be difficult due to the material’s strong hydrophobicity.