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Energy and Environment Research Division (ENE).

Research at PSI comprises all aspects of human energy use, with the ultimate goal of promoting development towards a sustainable energy supply system. Technologies are being advanced for the utilization of renewable energy sources, low-loss energy storage, efficient conversion, and low emission energy use. Experimental and model-based assessment of these emissions forms the basis of a comprehensive assessment of economic, environmental and social consequences, for both present and future energy supply systems.

Division Head: Prof. Dr. Alexander Wokaun

Scientific Highlights

22 February 2017


Ice-core evidence of earliest extensive copper metallurgy in the Andes 2700 years ago

Although copper (Cu) was essential for the wealth of pre- and post-colonial societies in the Andes, the onset of extensive Cu metallurgy in South America is still debated. Based on a 6500 year ice-core Cu record from Illimani glacier in Bolivia we provide the first complete history of large-scale Cu smelting activities in South America. Earliest anthropogenic Cu pollution was found during the Early Horizon period ~700-50 BC. We attribute the onset of intensified Cu smelting in South America to the activities of the central Andean Chiripa and Chavin cultures ~2700 years ago. This study provides for the first time substantial evidence for extensive Cu metallurgy already during these early cultures.

13 October 2016


Labile peroxides in secondary organic aerosol

Aerosols, suspended fine liquid or solid particles in the air we breathe, play a central role in many environmental processes through their influence on climate, the hydrological cycle, and their adverse effects on human health. While the mechanisms by which aerosol particles affect our health remain uncertain, the atmospheric oxidation of organic vapors has been shown to be related to the formation of oxygenated organic matter with high oxidative potential, the so-called reactive oxygen species (ROS). These species may damage our lung cells through oxidative stress. Also, if we want to understand the impact of human activity on our climate, we need to be able to reconstruct the conditions before the industrial era, and to determine the main ingredients responsible for the formation of aerosols and clouds. New results obtained from the cloud chamber at CERN revealed that new aerosol particles may originate from highly oxygenated organic molecules (HOMs). They are produced upon the oxidation of natural emissions and are composed of peroxides. This class of molecules seems to have important implications for climate and health.

7 July 2016



Media Releases Energy and Environment Renewable Energies

Despite its great potential, solar energy still faces one big problem: the sun doesn’t always shine and its energy is hard to store. Now, researchers at the Paul Scherrer Institute PSI and the ETH Zurich have unveiled a chemical process that uses the sun’s thermal energy to convert carbon dioxide and water directly into high-energy fuels: a procedure developed on the basis of a ground-breaking material combination of cerium oxide and rhodium.

24 May 2016


Organic Nitrate Contribution to New Particle Formation and Growth in Secondary Organic Aerosols from α-Pinene Ozonolysis

The chemical kinetics of organic nitrate production during new particle formation and growth of secondary organic aerosols (SOA) were investigated using the short-lived radioactive tracer 13N in flow-reactor studies of α-pinene oxidation with ozone. Direct and quantitative measurements of the nitrogen content indicate that organic nitrates accounted for ∼40% of SOA mass during initial particle formation, decreasing to ∼15% upon particle growth to the accumulation-mode size range (>100 nm). Experiments with OH scavengers and kinetic model results suggest that organic peroxy radicals formed by α-pinene reacting with secondary OH from ozonolysis are key intermediates in the organic nitrate formation process

10 March 2015


Pb pollution from leaded gasoline in South America in the context of a 2000-year metallurgical history

Exploitation of the extensive polymetallic deposits of the Andean Altiplano in South America since precolonial times has caused substantial emissions of neurotoxic lead (Pb) into the atmosphere; however, its historical significance compared to recent Pb pollution from leaded gasoline is not yet resolved. We present a comprehensive Pb emission history for the last two millennia for South America, based on a continuous, high-resolution, ice core record from Illimani glacier. Illimani is the highest mountain of the eastern Bolivian Andes and is located at the northeastern margin of the Andean Altiplano.

11 July 2014


Polychlorinated biphenyls in glaciers

We present a highly time-resolved historical record of polychlorinated biphenyls (PCBs) from an Alpine ice core (Fiescherhorn glacier, Switzerland). Introduced in the 1940s, PCBs were widely used industrial chemicals. Because of their persistence they are still found in the environment, long after their production phase-out. The Fiescherhorn ice core record covers the entire time period of industrial use of PCBs, that is, 1940?2002. The total concentration of six PCBs varies from 0.5 to 5 ng/L and reveals a temporal trend, with an 8-fold increase from the early 1940s to the peak value in the 1970s.

14 February 2014


Ice-core based assessment of historical anthropogenic heavy metal

The development of strategies and policies aiming at the reduction of environmental exposure to air pollution requires the assessment of historical emissions. Although anthropogenic emissions from the extended territory of the Soviet Union (SU) considerably influenced concentrations of heavy metals in the Northern Hemisphere, Pb is the only metal with long-term historical emission estimates for this region available, whereas for selected other metals only single values exist.

29 April 2013


Effect of surface charge density on the affinity of oxide nanoparticles

Using in-situ X-ray photoelectron spectroscopy at the vapor-water interface, the affinity of nanometer-sized silica colloids to adsorb at the interface is shown to depend on colloid surface charge density. In aqueous suspensions at pH 10 corrected Debye-Hückel theory for surface complexation calculations predict that smaller silica colloids have increased negative surface charge density that originates from enhanced screening of deprotonated silanol groups by counterions in the condensed ion layer.

7 February 2013


Chemistry: Ten things we need to know about ice and snow

Understanding the molecular behaviour of frozen water is essential for predicting the future of our planet, says Thorsten Bartels-Rausch.

17 December 2012


Variations in diesel soot reactivity along the exhaust after-treatment system, based on the morphology and nanostructure of primary soot particles

The reactivity of soot at different sites of the exhaust after-treatment system of a diesel engine (upstream and downstream of the diesel oxidation catalyst (DOC), downstream of the diesel particulate filter (DPF), as well as inside the DPF) was investigated on the basis of morphology and structure of primary soot particles by high resolution transmission electron microscopy (HRTEM). The results indicate that combustion-formed soot particles are susceptible to further transformations of their morphology within the exhaust system.

22 May 2012


Three centuries of eastern european and Altai lead emissions recorded in a belukha ice core

Human activities have significantly altered atmospheric Pb concentrations and thus, its geochemical cycle, for thousands of years. Whereas historical Pb emissions from Western Europe, North America, and Asia are well documented, there is no equivalent data for Eastern Europe. Here, we present ice-core Pb concentrations for the period 1680–1995 from Belukha glacier in the Siberian Altai, assumed to be representative of emissions in Eastern Europe and the Altai.

25 May 2011

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Gas uptake and chemical aging

Organic substances can adopt an amorphous solid or semisolid state, influencing the rate of heterogeneous reactions and multiphase processes in atmospheric aerosols. Here we demonstrate how molecular diffusion in the condensed phase affects the gas uptake and chemical transformation of semisolid organic particles. Flow tube experiments show that the ozone uptake and oxidative aging of amorphous protein is kinetically limited by bulk diffusion.

20 February 2011


long-lived reactive oxygen intermediates

The heterogeneous reactions of ozone with aerosol particles are of central importance to air quality. They are studied extensively, but the molecular mechanisms and kinetics remain unresolved. Based on new experimental data and calculations, we show that long-lived reactive oxygen intermediates (ROIs) are formed. The chemical lifetime of these intermediates exceeds 100 seconds, which is much longer than the surface residence time of molecular ozone (~ ns).

18 February 2011


Recent increase in black carbon concentrations
from a Mt. Everest ice core spanning 1860–2000 AD

A Mt. Everest ice core spanning 1860–2000 AD and analyzed at high resolution for black carbon (BC) using a Single Particle Soot Photometer demonstrates strong seasonality, with peak concentrations during the winter‐spring, and low concentrations during the summer monsoon season. BC concentrations from 1975–2000 relative to 1860–1975 have increased approximately threefold, indicating that BC from anthropogenic sources is being transported to high elevation regions of the Himalaya.

13 May 2010

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The nature of nitrate at the ice surface

Trace contaminants such as strong acids have been suggested to affect the thickness of the quasi-liquid layer at the ice/air interface, which is at the heart of heterogeneous chemical reactions between snowpacks or cirrus clouds and the surrounding air. We used X-ray photoelectron spectroscopy (XPS) and electron yield near edge X-ray absorption fine structure (NEXAFS) spectroscopy at the Advanced Light Source (ALS) to probe the ice surface in the presence of HNO3 at 230 K.

30 January 2010


The competition between organics and bromide at the aqueous solution – air interface as seen from ozone uptake kinetics and X-ray photoelectron spectroscopy

A more detailed understanding of the heterogeneous chemistry of halogenated species in the marine boundary layer is required. Here, we studied the reaction of ozone (O3) with NaBr solutions in presence and absence of citric acid (C6H8O7) under ambient conditions. Citric acid is used as a proxy for oxidized organic material present at the ocean surface or in sea spray aerosol.

1 January 2012

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DFT Modelling of Ru Nanoparticles Supported on Graphene and Graphite Surface: A Study of the B5 Active Sites Localisation

Carbon-supported Ruthenium catalysts exhibit very good catalytic properties, and are applied in the ammonia synthesis as well as for methanation processes e.g. in the gasification of wet biomass in super-critical water. Both reactions are known to be structure sensitive and require specific active sites at the catalyst. It has been found experimentally that mainly B5 sites are present and actively taking part in the catalytic reactions. Epitaxial growth of Ru on the carbon support can be considered following two orientations, one with the same orientation as the hexagonal carbon lattice, the other being rotated by 30° around the surface normal.


Supported gold as catalyst for the decomposition of ammonia precursors in the selective catalytic reduction of NOx

Titaniumdioxide supported gold was found to catalyze the hydrolysis of formate-based ammonia precursor compounds which are proposed for the selective catalytic reduction of nitrogen oxides (NOx) in combustion exhaust gas. In contrast to other noble metals, the supported gold does not oxidize the released NH3, while it maintains decomposition of intermediate formic acid.

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Influence of Methyl Halide Treatment on Gold Nanoparticles Supported on Activated Carbon

Gold particles supported on carbon when subjected to a flow of methyl iodide or bromide redisperse from large ensembles to single atoms and/or dimers of gold. Methyl halide oxidizes gold leading to gradual particle dissolution. The process could be carried out at temperatures as low as 50 °C. The excess of halide could be removed by a post-treatment of the material with 1%H2O/H2, which does not influence the metal dispersion. This remarkable transformation opens the possibility of re-activating gold catalysts that lost their performance due to metal particles sintering.


Identification of the SCR active sites in Fe-ZSM-5

he identification of the SCR active sites in Fe-ZSM-5 is of utmost importance for the understanding and optimization of the catalyst performance. No method (e.g. UV/VIS, IR, EPR, EXAFS, XPS, XRD) can definitively distinguish between isolated iron species and iron oxide clusters of different nuclearity in the same sample. A statistical approach was used to solve this problem. From the correlation of the measured SCR activity with the calculated concentration of different species the temperature dependent activities of isolated, dimeric and oligomeric iron species and iron particles could be determined.


Vibrational Spectra of Adsorbates from DFT

The hydrolysis of isocyanic acid was studied experimentally and theoretically and a reaction mechanism on different catalysts was established. The decreasing NOx emission limits for diesel vehicles impel the further development of the existing NOx deactivation technologies, particularly the selective catalytic reduction (SCR) of nitrogen oxides with urea. In the urea-SCR process, urea is injected into the hot exhaust gas, where it thermally decomposes into isocyanic acid (HNCO) and ammonia.


Dosing Differential Electrochemical Mass Spectrometry (D-DEMS) for Li-O2 Batteries

he high-energy rechargeable Li-O2 battery has been subject to intensive research worldwide during the past years. The Li-O2 cell mainly comprises a negative (e.g. Li metal) and positive (e.g. porous carbon) electrode separated by an electronically insulating, but Li+ conducting electrolyte layer. In order to study the cell chemistry, a differential electrochemical mass spectrometry setup based on a set of valves, a pressure sensor and a quadrupole mass spectrometer has been developed.

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Radiation grafted membranes developed at PSI outlast state-of-the art commercial membranes in the fuel cell

Components for the polymer electrolyte fuel cell (PEFC) are required to show high performance and durability under application relevant conditions. Furthermore, for commercial viability the materials and processes for component fabrication need to be of los cost. The polymer electrolyte membrane developed at PSI on the basis of the radiation grafting technique has the potential of being produced in cost-effective manner. In recent years, we have collaborated with the Belenos Clean Power to further develop the membrane to commercial competitiveness.


Partially reduced graphene oxide paper: a thin film electrode for electrochemical capacitors

One way to utilize graphene and its’ outstanding specific surface area of 2630 m2g-1 for supercapacitor electrodes is by preparing a so called free-standing graphene paper. Such a flexible, conductive graphene-paper electrode was prepared by a flow-directed filtration of graphene oxide dispersion followed by a gentle thermal reduction treatment of the filtrate. The prepared partially reduced graphene oxide paper (GOPpr) showed a dense packing of graphene sheets with a distinct interlayer distance of 4.35 Å.


Flow modeling in gas diffusion layers of PEFCs at the micro- and mesoscale

he optimization of thermochemical and electrochemical conversion systems is of high importance for a sustainable energy future society. Of particular interest regarding the performance of polymer electrolyte fuel cells (PEFCs) is the study of the gas flow in the gas diffusion layers (GDL). More specifically, permeability and diffusivity measurements in a model PEFC under normal operating conditions are highly desirable. As laboratory-measurements of these quantities under such conditions are very demanding, an alternative is the use of computer-based simulations.


X-Ray Tomography of Water in Operating Fuel Cell

Polymer electrolyte fuel cells (PEFC) convert the chemical energy of hydrogen with a high efficiency (40-70 %) directly into electricity. The product of the overall reaction is water, produced at the cathode of the cell. The interaction of liquid water with the porous structures of the cell is one of the mechanisms in the PEFC that are commonly believed to be key for further optimization with regard to performance, durability and cost.


Local current measurement in PEFCs

Major barriers for a successful commercialization of Polymer Electrolyte Fuel Cells (PEFCs) are insufficient lifetime and high cost of platinum catalyst. A comprehensive understanding of aging and transport phenomena on all relevant length scales is a key to improve durability and to reduce precious metal loading. Flow fields as used in PEFCs for the distribution of the reactant gases over the electrode area cause inhomogeneities. The importance of down the channel inhomogeneities has been realized.

29. June 2015

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Particulate matter from modern gasoline engines damages our lungs

Media Releases Environment Energy and Environment

For years, studies have proved that fine dust from petrol engines can damage our health. Modern engine technology does not help, either, as researchers from the University of Bern and the Paul Scherrer Institute (PSI) reveal.

17. September 2014


Airpocalypse explained

Media Releases Environment Energy and Environment

The causes of China's record level fine particulate pollution in winter 2013
At the beginning of 2013 a greyish-brown blanket of smog lay over large areas of China for several months. The fine particle pollution was higher by 1 to 2 orders of magnitude than the levels normally measured in Western Europe and the United States. An international team of researchers under the lead of the Paul Scherrer Institute PSI and the Institute of Earth Environment, Chinese Academy of the Sciences revealed the causes of the airpocalypse. The study published in the journal Nature also describes what steps are to be taken to prevent an environmental crisis of this kind in the future.

13. May 2014


Unassuming rampant polluters on two wheels

Media Releases Energy and Environment Environment

In some towns small mopeds cause more air pollution than cars

Not cars or trucks, but mopeds with their two-stroke engines are the main source of fine particles and other air contaminants in many towns in Asia, Africa and southern Europe. This is revealed by the study of an international research team headed up by researchers at the Paul Scherrer Institute PSI. The reasons for the high emissions are the combustion properties in two-stroke engines and the overly lenient emission requirements for small two-wheelers. The study findings are to be published on 13 May 2014 in the journal Nature Communications.

17. December 2013


Experiments in the clouds – how soot influences the climate

Media Releases Energy and Environment Environment

PSI-researcher Martin Gysel receives prestigious European funding (ERC Consolidator Grant) for his studies on the role of soot in cloud formation and global warming.

6. October 2013


Particle formation in the atmosphere – further aspect unveiled via the CLOUD experiment at CERN

Media Releases Energy and Environment Environment

Clouds consist of cloud droplets that are formed from tiny particles floating in the atmosphere. How these particles develop, however, largely remains a mystery. The formation of particles from amines and sulphuric acid has now been described for the first time – a milestone in atmospheric research.

19. April 2010

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The mass concentration of volcanic ash from Iceland in European airspace

Media Releases Energy and Environment Environment

Data of the Paul Scherrer Institute from the High-Alpine Research Station Jungfraujoch yield important information.
The eruption of the volcano Eyjafjallajokull in Iceland has stalled flight traffic in large parts of Europe. Decision makers had to base their decisions mainly on model calculations for the volcanic plume dispersion. How dangerous is this volcanic ash layer for planes?

18. January 2010

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News from the smog chamber: mechanisms of particle formation in the atmosphere unveiledt

Media Releases Environment Energy and Environment

Up to the present time, the nucleation or new formation of particles in the atmosphere has been a great enigma. Until recently, research was based on the assumption that sulphuric acid played the central role in particle formation. However, laboratory experiments and field tests have consistently provided conflicting results. In the lab, considerably higher concentrations of sulphuric acid are required for nucleation to take place than in the atmosphere itself. Now scientists from the Paul Scherrer Institute (PSI) have found out the cause for these conflicting results from their smog chamber. These findings will advance climate research to a significant degree.

10. December 2009

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Mystery solved: how fine particulates are formed in the air

Media Releases Environment Energy and Environment

Researchers from the Paul Scherrer Institute, the University of Colorado and 29 other research institutions in various countries have investigated the composition of the organic constituents of the fine particulates found in various regions of the world, and have identified the original substances from which they are formed in each case. For the first time ever, this has enabled them to explain the role played by the individual components of emissions in the development of fine particulates.

8 November 20

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CCN formation mechanism in lower troposphere needs revision

Atmospheric aerosols exert an important influence on climate1 through their effects on stratiform cloud albedo and lifetime and the invigoration of convective storms. Model calculations suggest that almost half of the global cloud condensation nuclei in the atmospheric boundary layer may originate from the nucleation of aerosols from trace condensable vapours, although the sensitivity of the number of cloud condensation nuclei to changes of nucleation rate may be small. Despite extensive research, fundamental questions remain about the nucleation rate of sulphuric acid particles and the mechanisms responsible, including the roles of galactic cosmic rays and other chemical species such as ammonia. Here we present the first results from the CLOUD experiment at CERN.