Difficulty: Introductory | Prerequisites: General Chemistry I (atomic structure, bonding, basic thermodynamics)
Sustainable energy is one of the defining challenges of the century, and chemistry sits at its core. Every solar cell, battery and fuel cell is a chemical system, so advances in materials science and electrochemistry translate directly into cleaner, cheaper energy. This topic bridges organic chemistry with applied energy science: you need a working understanding of bonding, redox reactions and thermodynamics to follow the material. If you have been focusing on reaction mechanisms so far, this is where you see those ideas applied at industrial scale.
Chemistry underpins every major sustainable-energy technology: batteries store renewable energy through electrochemical reactions, fuel cells convert hydrogen into electricity, and solar cells turn photons into current using semiconductor materials. Current research focuses on raising efficiency, cutting costs and finding abundant replacement materials such as perovskites and graphene.
Lithium-ion battery
A rechargeable battery that shuttles lithium ions between an anode and a cathode through an electrolyte. The dominant chemistry in portable electronics and electric vehicles.
In simple terms, it is the rechargeable battery in your phone and laptop. Lithium ions move back and forth, and that movement is what stores and releases energy.
Fuel cell
An electrochemical device that converts the chemical energy of a fuel (typically hydrogen) directly into electricity and water, without combustion.
Think of it as a battery that never runs flat, so long as you keep feeding it hydrogen. The output is electricity plus water, with no exhaust gases.
Photovoltaic cell (solar cell)
A semiconductor device that converts photons from sunlight into an electric current via the photovoltaic effect.
In simple terms, sunlight knocks electrons loose in a silicon wafer, and those moving electrons become the current that powers your house.
Thin-film solar cell
A solar cell made by depositing one or more thin layers of photovoltaic material onto a substrate such as glass or plastic. Uses far less semiconductor material than conventional crystalline-silicon cells.
Think of it as painting a very thin coat of solar material onto a surface instead of cutting a thick silicon wafer.
Perovskite
A class of materials with a specific crystal structure (ABX₃) that has shown rapid efficiency gains as a photovoltaic absorber. Named after the mineral, not a single compound.
In simple terms, perovskites are a family of crystals that absorb sunlight well and are cheap to make, which is why researchers are excited about them for next-generation solar panels.
Graphene
A single layer of carbon atoms arranged in a two-dimensional hexagonal lattice. Exhibits exceptional electrical conductivity, mechanical strength and surface area.
Think of it as a sheet of chicken wire made entirely of carbon atoms, one atom thick. Its huge surface area makes it promising for batteries and supercapacitors.
Supercapacitor
An energy-storage device that stores charge electrostatically on the surface of electrode materials, rather than through chemical reactions. Charges and discharges much faster than a battery, but stores less total energy.
In simple terms, a supercapacitor is like a very fast, very shallow bucket: it fills and empties quickly, but does not hold as much as a battery.
Energy density
The amount of energy stored per unit mass (gravimetric, Wh/kg) or per unit volume (volumetric, Wh/L) of a storage device.
In simple terms, it tells you how far an electric car can drive on a battery of a given weight. Higher energy density means more range for less mass.
Catalyst
A substance that increases the rate of a chemical reaction without being consumed. In energy applications, catalysts lower the energy barrier for reactions inside fuel cells and emission-control systems.
Think of it as a matchmaker for molecules: it helps them react more easily without getting used up itself.
The central problem: solar and wind are intermittent, so energy must be stored chemically for use when the sun is not shining or the wind is not blowing.
Lithium-ion batteries are the current workhorse. First developed in the 1970s, they now power smartphones, laptops and electric vehicles.
Active research targets:
Higher energy density (more stored energy per kilogram)
Longer cycle life (more charge/discharge cycles before degradation)
Lower cost through cheaper electrode and electrolyte materials
Graphene and other carbon nanomaterials are being explored as electrode materials because of their enormous surface area and conductivity.
Supercapacitors complement batteries where rapid charge/discharge is needed, though they store less total energy.
A fuel cell converts chemical energy directly to electricity. The most common type uses hydrogen as fuel: H₂ is oxidised at the anode, O₂ is reduced at the cathode, and the only by-product is water.
Advantages over combustion engines: higher thermodynamic efficiency (no Carnot limit in the same way) and zero tailpipe emissions when running on pure hydrogen.
Chemistry challenges:
Platinum-group catalysts are effective but expensive and scarce. Researchers are developing catalysts from cheaper, more abundant metals.
Membrane durability: proton-exchange membranes degrade over time, limiting fuel-cell lifespan.
Hydrogen storage and transport remain practical obstacles.
Conventional cells use crystalline silicon. When photons strike the semiconductor, they excite electrons across the band gap, generating current.
Thin-film solar cells deposit a much thinner layer of photovoltaic material (e.g. cadmium telluride, CIGS) onto glass or plastic, cutting material costs.
Perovskite solar cells have jumped from about 3% efficiency in 2009 to over 25% in laboratory settings, a pace of improvement unmatched by any other photovoltaic technology.
Outstanding problems:
Perovskites degrade quickly when exposed to moisture and UV light. Stability is the main barrier to commercialisation.
Scaling lab results to factory production without losing efficiency.
Even with renewables growing, fossil fuels remain a major energy source. Chemistry contributes by:
Developing catalysts that convert harmful exhaust gases (NOₓ, CO, unburnt hydrocarbons) into less harmful products. This is the chemistry behind catalytic converters.
Improving combustion efficiency so less fuel produces the same energy output.
Carbon-capture chemistry: materials and reactions that pull CO₂ from flue gas or ambient air.
Graphene: a single layer of carbon atoms with exceptional conductivity and mechanical strength. Potential applications in battery electrodes, supercapacitor electrodes and transparent conductive films for solar cells.
Perovskites: as noted above, their tuneable band gap and cheap precursors make them one of the most actively researched photovoltaic materials.
Metal-organic frameworks (MOFs) and other porous materials are being studied for hydrogen storage and CO₂ capture.
The common thread: chemistry is not just optimising existing devices but discovering entirely new classes of material that change what is possible.
Batteries: Every electric vehicle on the road runs on lithium-ion chemistry. Grid-scale battery farms (e.g. Tesla Megapack installations) store surplus solar and wind energy and release it during peak demand.
Fuel cells: Hydrogen fuel-cell buses and lorries are already in commercial service in several countries. Fuel cells also provide backup power for data centres and hospitals.
Solar cells: Rooftop photovoltaic panels are the most visible application. Thin-film cells are used in building-integrated photovoltaics, where the solar material is part of the window glass or facade.
Catalysis: The catalytic converter in every petrol and diesel car uses platinum-group catalysts to scrub exhaust gases, the same class of catalyst chemistry that fuel-cell researchers are trying to replace with cheaper alternatives.
Students often assume fuel cells "generate" energy. They do not. They convert the chemical energy already present in the fuel. The energy has to come from somewhere (e.g. producing the hydrogen in the first place).
A common error is treating solar-cell efficiency and cost as the same problem. A cheap cell with modest efficiency can still be more economical than an expensive high-efficiency cell, depending on the application.
Students sometimes conflate energy density with power density. Energy density is how much total energy a device stores; power density is how quickly it can deliver that energy. Supercapacitors have high power density but low energy density relative to batteries.
Perovskites are not a single material. The term refers to a crystal structure (ABX₃) that many different compounds can adopt. Which perovskite you choose changes the band gap, stability and toxicity profile.
⚠️ Be ready to explain the basic electrochemistry of a lithium-ion battery: what moves (Li⁺ ions), where (anode to cathode on discharge, reverse on charge) and why (difference in electrode potential).
⚠️ Know the distinction between a fuel cell and a battery. A fuel cell requires a continuous external fuel supply; a battery stores its reactants internally.
⚠️ Expect a question linking the photovoltaic effect to semiconductor band-gap theory. If you cannot explain what a band gap is and why it matters for solar-cell efficiency, review that first.
⚠️ The role of catalysts in both fuel cells and emission control is a frequent exam topic. Be able to name what a catalyst does (lowers activation energy) and why platinum is used (high catalytic activity, stability) and why researchers want alternatives (cost, scarcity).
⚠️ Perovskite solar cells are a common "recent advances" exam question. Know the ABX₃ structure, why efficiency has risen so fast, and what the main barrier to commercialisation is (stability under moisture and UV).
True or false: A fuel cell generates energy from nothing, much like a perpetual-motion machine. (False. It converts chemical energy from an external fuel supply.)
Fill in the blank: The photovoltaic effect occurs when ______ from sunlight knock electrons across the ______ of a semiconductor. (photons; band gap)
True or false: Graphene is a multi-layered carbon structure similar to diamond. (False. Graphene is a single layer of carbon atoms in a hexagonal lattice.)
Fill in the blank: A supercapacitor has high ______ density but low ______ density compared with a lithium-ion battery. (power; energy)
True or false: Perovskite refers to one specific chemical compound. (False. It refers to any compound with the ABX₃ crystal structure.)
Q: Explain why energy storage is a critical challenge for renewable energy sources such as solar and wind.
A: Solar and wind are intermittent: they produce energy only when the sun shines or the wind blows. Without storage, surplus energy is wasted and demand during low-production periods goes unmet. Batteries and other storage technologies bridge this gap by converting electrical energy into chemical energy that can be released on demand.
Q: Describe the basic operating principle of a hydrogen fuel cell and name its primary by-product.
A: Hydrogen gas is oxidised at the anode, releasing electrons that travel through an external circuit (producing electricity) and protons that pass through a membrane to the cathode. At the cathode, oxygen is reduced and combines with the protons and electrons to form water, which is the primary by-product.
Q: What distinguishes thin-film solar cells from conventional crystalline-silicon solar cells?
A: Thin-film cells deposit a very thin layer of photovoltaic material (often just a few micrometres) onto a substrate such as glass or plastic, using far less semiconductor material than the thick wafers in conventional crystalline-silicon cells. This makes them cheaper to produce, though historically at the cost of lower efficiency.
Q: Why are perovskite materials considered promising for next-generation solar cells, and what is the main obstacle to their commercialisation?
A: Perovskites have shown rapid efficiency gains (from roughly 3% to over 25% in about a decade), their precursor materials are cheap, and their band gap is tuneable. The main obstacle is stability: perovskite cells degrade quickly when exposed to moisture and UV radiation, limiting their practical lifespan.
Q: Distinguish between energy density and power density and give one device example for each.
A: Energy density measures total energy stored per unit mass or volume. Power density measures how quickly that energy can be delivered. A lithium-ion battery has high energy density (stores a lot of energy, releases it gradually). A supercapacitor has high power density (delivers energy in rapid bursts, but stores less overall).
Q: Name two ways chemistry contributes to reducing the environmental impact of fossil fuels.
A: First, catalysts in catalytic converters transform harmful exhaust gases (CO, NOₓ, unburnt hydrocarbons) into less harmful products (CO₂, N₂, H₂O). Second, carbon-capture chemistry uses materials and reactions to remove CO₂ from flue gas or the atmosphere, reducing net emissions.
This material connects directly to electrochemistry (redox half-reactions, electrode potentials, Nernst equation), which you will need for any detailed battery or fuel-cell question. It also ties into solid-state chemistry and materials science, particularly band-gap theory for solar cells and crystal-structure classification for perovskites. If you are also covering thermodynamics, the efficiency limits of fuel cells versus heat engines (Carnot efficiency) make a good comparison point.
sustainable energy chemistry, lithium-ion battery chemistry, fuel cell electrochemistry, photovoltaic effect, solar cell materials, thin-film photovoltaics, perovskite solar cells, ABX₃ crystal structure, graphene energy storage, supercapacitor vs battery, energy density vs power density, catalytic converter chemistry, carbon capture, green chemistry, renewable energy storage, hydrogen economy, proton-exchange membrane, band gap semiconductor, electrochemistry redox, Organic Chemistry II University of Michigan