EES Blog

A new type of blue energy harvesting device may offer a practical method of continuous coastal electricity generation.

In 2011, Stanford researchers described a new form of energy harvesting device coined as a “mixing entropy battery” in Nano Letters¹. Their device capitalized on the chemical energy available in a system where an ion concentration gradient is present; in this case where low salinity wastewater or river water was mixed with ~0.6 M NaCl rich seawater. It is estimated that during this mixing process, there is a free energy reduction of 2.2 kJ per liter of freshwater.

Extractable energy depends on charging time

Efforts towards a less energy and environmentally intensive method for CO₂ capture has resulted in a novel porous polymer with noteworthy performance.

Current industrial standards for carbon dioxide scrubbing in coal-fired power plants utilize an energy intensive liquid amine process to reduce CO₂ gas emissions. Ultimately, a technology that can reduce the energy input required to release captured CO₂ while maintaining substantial adsorption selectivity and capacity would be ideal. Investigations performed at Texas A&M have demonstrated high adsorption capacities of 1.7 mmol CO₂ /g polymer with a gas flow comprised of 15% CO₂ / 85% N₂ under ambient conditions.

This work is the fruit of grafting NH₄ groups to the sulfonate sites on a porous polymer network that was previously published, which leads to a higher selectivity to CO₂ over N₂ and CH₄ gases also present in the exhaust streams of coal-fired power plants. Further improvements in adsorption capacity, while reducing the temperature required to remove the captured gas, can eventually yield a cheaper, more environmentally friendly alternative for greenhouse gas sequestration.

Interested? Read the full communication in Energy and Environmental Science here:

Building multiple adsorption sites in porous polymer networks for carbon capture applications
Weigang Lu, Wolfgang M. Verdegaal, Jiamei Yu, Perla B. Balbuena, Hae-Kwon Jeong and Hong-Cai Zhou
DOI: 10.1039/C3EE42226G

Researchers have demonstrated the use of doped graphene to improve the photoelectrochemical production of hydrogen.

In a novel approach, a monolayer of graphene has been reported as an effective catalyst towards the hydrogen evolution reaction (HER). By depositing a single layer of graphene on a p-doped silicon photocathode, the overpotential required for the HER in the presence of light was shifted positively by 0.18 V vs. RHE. The catalytic activity was confirmed to be a result of the graphene layer by testing on a glassy carbon substrate, where a 50 mV shift in onset compared to glassy carbon baseline was discovered.

This transparent catalyst monolayer was also shown to act as a passivation layer, preventing oxidation of the substrate while maintaining current density. This led to a more consistent onset potential when compared to the bare Si photocathode, which degraded over time quite substantially. Furthermore, by treating the graphene layer in nitrogen plasma, the added defects, as well as the nitrogen doping, led to even further improvements in catalytic activity towards HER.

As a proof of concept, platinum was added to the N-doped graphene monolayer, where a solar-to-hydrogen conversion efficiency of 3.05% was reported, which maintained activity over a range of pH. With further optimizations, carbon based catalysts can contend as a cost effective method for the clean production of hydrogen on a commercial scale.

Interested? Read the full communication in Energy and Environmental Science here:

N-doped monolayer graphene catalyst on silicon photocathode for hydrogen production
Uk Sim, Tae-Youl Yang, Joonhee Moon, Junghyun An, Jinyeon Hwang, Jung-Hye Seo, Jouhahn Lee, Kye Yeop Kim, Joohee Lee, Seungwu Han, Byung Hee Hong and Ki Tae Nam
Energy Environ. Sci., 2013, Paper
DOI: 10.1039/C3EE42106F