We are surrounded by surfaces. Processes and interactions taking place at these surfaces affect a multitude of aspects of our lives. Even in the combat of a macroscopic phenomenon, such as climate change and a sustainable energy system, surface properties and processes taking place both at the macro- and the nanoscale, have important roles to play.
The energy system comprises all components from primary energy sources like fossil fuels and water dams, via harvesting, conversion, transport, storage and ultimate use of the energy. It also includes waste and pollutants from the system and regulations, taxes and legal aspects to promote or de-promote desired/undesired effects.
Surface science is an enabling technology in many areas and that of energy is no exception. Striving towards a more sustainable energy system, surfaces properties and interactions, and reactions taking place at surfaces, have key roles to play. Examples are found in the production, storage and use of energy, in the reduction of environmentally harmful gases and for reduction of climate affecting CO2-emission.
Sources of renewable energy is a mandatory component in a sustainable energy system. A key such source is the sun. The solar energy can be harvested, e.g., for electrical energy production via photovoltaics. In these applications, the surface properties and conditions of the optical components are critical for optimal performance, and they can be tailored to have special optical properties that are important for the solar cells.
Another example is catalytic and photo- and electrocatalytic processes for generation of fuels, for example biofuel production and refining, and hydrogen production. In photocatalytic hydrogen production, still mainly at the research level, solar photons excite hot electrons in the surface region of the photocatalyst, which then induce dissociation of water molecules to hydrogen (H2) and O2. The hydrogen then becomes an energy storage medium that can later be used for conversion to electricity (see below).
Energy in the form of electricity, can also be produced in fuel cells with hydrogen as energy source. This process is critically depending on surface properties because only a few surfaces can convert the chemical energy stored in H2 into electrical energy in a process that essentially is the reverse of the process described above for H2 production.
Surfaces are also important for construction materials in energy systems. An obvious example is that the materials need to be corrosion resistant in the, sometimes harsh, environments of energy system components. Corrosion and corrosion inhibitors are typical surface phenomena. Another example is the problem of icing of windmills. It is then desirable to have surfaces that deice or don’t form ice coatings. Deicing of surfaces is a typical surface science problem, related to surface properties such as (super)hydrophobicity and hydrophilicity and water/ice nucleation on surfaces. Yet another example related to materials and surface science is tribology in moving parts of energy devices, such as turbines, pistons and piston rings, and in fly wheels. Lubrication, friction and wear of surfaces are the central phenomena in tribology and surface science has in a major way contributed to this field of science and engineering.
As the availability of some renewable energy sources, like radiation from the sun and the wind, fluctuates throughout the day, energy storage is an important part of a sustainable energy system. Energy storage is also increasingly important to support the shift from fossil powered vehicles to e.g. electrical or hydrogen powered ones.
Surfaces are functional in electrical storage devices such as in e.g. batteries and super capacitors. Hydrogen storage, which as we mentioned above also works as energy storage medium, involves typical surface properties such as adsorption, desorption and diffusion. Fuel cells, which are converters of fuels to electricity, involve many elementary surface steps such as adsorption, surface dissociation, and desorption.
Storage of solar energy can be performed in batteries but also by converting solar radiation into fuels by photocatalytic processes. Photocatalysis is an own field of surface science involving both the absorption of light in surfaces and conversion of photons into hot charge carriers that can help producing fuels, e.g. by splitting water into hydrogen and oxygen.
In fossil fueled cars the three main pollutants are CO, hydrocarbons and NOx. The area of heterogenous catalysis has reduced these emissions by the so called three-way catalytic converter. This development, where surface science has played a major role, has taken place over more than half a century. It has dramatically reduced environmental pollution by converting CO to CO2, hydrocarbons to CO2 and water and NOx to N2 over supported catalysts mainly consisting of a porous ceramic support and active noble metal catalyst nanoparticles on the support (Pt, Rh, Pd,…)
Surface science is also important in climate-influencing technologies that can help us decarbonize industry and reduce the emissions of CO2 into the atmosphere. The major source of CO2 emissions is the transport sector, due to its total dependence on fossil fuels, but also electricity production in coal or gas powered power plants is a large contributor as is production of steel and concrete.
One specific example of how surface science come into play is CCS, carbon capture and storage. In this technology, where CO2 is captured, transported and stored, surface properties and surface interactions can play a role both in the capture step and in the storage step. In the first step, surfaces are involved via e.g. adsorption on tailored CO2-adsorbent materials, which is one way to capture CO2 . In the storage step, the surface properties of the storage site are important. One way to finally store the captured CO2 is to trap it deep down in geological formations such as saline aquifers and depleted oil and gas reservoirs, and the storage capacity of the site depends on the capillary pressure of the sealing rock . Other, more futuristic technologies attempt to convert captured and stored CO2 to useful fuels by using solar light and photocatalysts – also typical surface phenomena.
Learn more about how surface science helps us in the endeavor towards sustainable energy solutions in our podcast, Science on surfaces – a bigger perspective on the small. In this episode, we talk about the bigger picture of climate change and the energy system.
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