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Intro to Chemistry
Table of Contents
Unit 17 Overview: Electrochemistry
17.1 Review of Redox Chemistry
17.2 Galvanic Cells
17.3 Electrode and Cell Potentials
17.4 Potential, Free Energy, and Equilibrium
17.5 Batteries and Fuel Cells
17.6 Corrosion
17.7 Electrolysis

Batteries and fuel cells are electrochemical powerhouses that convert chemical energy into electrical energy. They rely on redox reactions, with electrons flowing from the anode to the cathode through an external circuit, while ions move through the electrolyte.

Rechargeable batteries offer eco-friendly, cost-effective power solutions, but have limitations like longer charging times. Fuel cells boast higher efficiency than combustion engines, producing only water as a byproduct. Both technologies play crucial roles in our energy landscape.

Batteries and Fuel Cells

Components of common batteries

  • Anode (negative electrode) oxidizes releases electrons to the external circuit (zinc in alkaline batteries)
  • Cathode (positive electrode) reduces accepts electrons from the external circuit (manganese dioxide in alkaline batteries)
  • Electrolyte allows the flow of ions between the anode and cathode can be a liquid, gel, or solid (potassium hydroxide in alkaline batteries)
  • Separator prevents direct contact between the anode and cathode allows the flow of ions through the electrolyte (polyethylene in lithium-ion batteries)
  • Electrodes (both anode and cathode) are the sites where electrochemical reactions occur

Electrochemistry in batteries and fuel cells

  • Redox reactions drive the energy conversion process in batteries and fuel cells
  • Cell potential (also known as electromotive force) determines the voltage output of the battery or fuel cell
  • Nernst equation relates the cell potential to the concentrations of reactants and products
  • Faraday's laws of electrolysis describe the quantitative aspects of electrochemical reactions

Fuel cells vs combustion engines

  • Fuel cells convert chemical energy directly into electrical energy have higher efficiency (40-60%) compared to combustion engines produce water as the only byproduct operate quietly and continuously as long as fuel is supplied (hydrogen fuel cells)
  • Traditional combustion engines convert chemical energy into mechanical energy through combustion have lower efficiency (20-40%) produce various pollutants (CO, NOx, unburned hydrocarbons) operate noisily and are limited by the Carnot cycle efficiency (gasoline engines)

Advantages of rechargeable batteries

  • Reusable can be recharged multiple times reduces waste and environmental impact (lithium-ion batteries)
  • Cost-effective in the long run saves money compared to constantly replacing non-rechargeable batteries
  • Convenient no need to constantly replace batteries easy to maintain and use
  • High energy density stores more energy per unit volume compared to non-rechargeable batteries (nickel-metal hydride batteries)
  • Limitations include higher initial cost, longer charging time, limited charge cycles, potential for overheating or explosion if damaged or improperly used, and environmental concerns regarding disposal and extraction of rare earth metals

Key Terms to Review (42)

Alkaline batteries: Alkaline batteries are a type of primary battery dependent on the reaction between zinc and manganese dioxide. They are known for their long shelf life and stable voltage output.
Battery: A battery is a device consisting of one or more electrochemical cells that convert stored chemical energy into electrical energy. It typically has a positive (cathode) and negative (anode) terminal.
Active electrodes: Active electrodes are the electrodes in an electrochemical cell where the redox reactions occur. They participate directly in the chemical reactions by either gaining or losing electrons.
Anode: The anode is the electrode where oxidation occurs in a galvanic cell. It is typically the negative terminal in such cells.
Cell potentials, Ecell: Cell potential, denoted as $E_{cell}$, is the measure of the electromotive force (emf) of an electrochemical cell. It represents the potential difference between the two electrodes.
Electrolysis: Electrolysis is a chemical process in which electrical energy is used to drive a non-spontaneous chemical reaction. It involves passing an electric current through an electrolyte, causing ions to move and resulting in the deposition of substances at the electrodes.
Dry cell: A dry cell is a type of electrochemical cell that uses a low-moisture paste as an electrolyte, allowing it to operate in any orientation without spilling. It is commonly used in portable electronic devices.
Electron volts (eV): An electron volt (eV) is a unit of energy equal to the amount of kinetic energy gained by an electron when it is accelerated through an electric potential difference of one volt. It is commonly used in nuclear and particle physics to express small amounts of energy.
Electrolytes: Electrolytes are substances that dissociate into ions when dissolved in water, allowing the solution to conduct electricity. Common examples include salts, acids, and bases.
Fuel cell: A fuel cell is an electrochemical device that converts the chemical energy of a fuel, such as hydrogen, directly into electricity through a reaction with oxygen. Unlike batteries, fuel cells require a continuous supply of fuel and oxidant to sustain the chemical reaction.
Half-reaction: A half-reaction is either the oxidation or reduction component of a redox reaction. It shows the loss or gain of electrons by a species.
Lead acid battery: A lead acid battery is a type of rechargeable battery that uses lead dioxide and sponge lead for its electrodes, with sulfuric acid as the electrolyte. It is commonly used in automotive applications and uninterruptible power supplies.
Primary cells: Primary cells are electrochemical cells that generate electrical energy from spontaneous redox reactions and cannot be recharged. Once the chemical reactants are exhausted, they must be disposed of or recycled.
Secondary cells: Secondary cells are rechargeable batteries that can be recharged and used multiple times. They undergo reversible chemical reactions to restore their charge.
Half-Reaction: A half-reaction is the oxidation or reduction of a single element or compound that occurs during a redox (reduction-oxidation) reaction. It represents the individual processes of losing or gaining electrons that take place on each side of a balanced chemical equation.
Electrochemistry: Electrochemistry is the study of the relationship between electrical energy and chemical energy, and the interconversion between the two. It involves the study of chemical reactions that produce electricity and the use of electrical energy to drive chemical reactions.
Separator: A separator is a device or material used in batteries and fuel cells to physically and electrically isolate the anode and cathode, preventing direct contact while still allowing the flow of ions between them. It is a critical component that ensures the safe and efficient operation of these electrochemical energy storage and conversion systems.
Electrolyte: An electrolyte is a substance that, when dissolved in a solvent such as water, dissociates into charged particles called ions. These ions are capable of conducting electricity and are essential for various chemical and physiological processes in the body and in electrochemical devices.
Cell Potential: Cell potential, also known as electrochemical potential or redox potential, is a measure of the driving force or tendency for a chemical reaction to occur in an electrochemical cell. It represents the potential difference between the two electrodes in a galvanic cell, which determines the spontaneity and direction of the redox reaction.
Potassium hydroxide: Potassium hydroxide, also known as caustic potash, is a strong alkaline compound that is widely used in various industrial and chemical applications. It is a white, crystalline solid that readily dissolves in water, producing a highly basic solution.
Nernst Equation: The Nernst equation is a fundamental relationship in electrochemistry that describes the relationship between the reduction potential of an electrochemical half-reaction and the activities of the chemical species involved. It is a crucial tool for understanding and predicting the behavior of galvanic cells, electrode potentials, and the spontaneity of electrochemical processes.
Anode: The anode is the electrode in an electrochemical cell where oxidation occurs, and electrons are released to flow through an external circuit. It is the negatively charged electrode that attracts positively charged ions and initiates the flow of electrons in a redox reaction.
Volt: The volt (symbol: V) is the derived unit for electric potential difference and electromotive force in the International System of Units (SI). It is named after the Italian physicist Alessandro Volta, who invented the first electric battery. The volt is the potential difference across a resistance of one ohm when a current of one ampere is flowing through it.
Zinc: Zinc is a metallic element that plays a crucial role in various biological processes within the human body. It is an essential mineral required for the proper functioning of numerous enzymes and is involved in a wide range of physiological activities, including immune system function, wound healing, and protein synthesis.
Electrode: An electrode is a conductor used to make contact with a nonmetallic part of an electrical circuit, such as an electrolyte solution or a semiconductor. It is a critical component in various electrochemical processes, including those involved in batteries, fuel cells, and the measurement of cell potentials.
Hydrogen Fuel Cells: Hydrogen fuel cells are electrochemical devices that convert the chemical energy of hydrogen and oxygen into electrical energy, producing water as the only byproduct. They serve as efficient and clean energy sources, making them a promising alternative to traditional fossil fuel-based power generation.
Lithium-ion Batteries: Lithium-ion batteries are a type of rechargeable battery that use lithium ions as the main component for energy storage and conversion. They are widely used in various electronic devices, electric vehicles, and energy storage systems due to their high energy density, long lifespan, and low maintenance requirements.
Redox Reaction: A redox (reduction-oxidation) reaction is a type of chemical reaction that involves the transfer of electrons between two or more reactants. In a redox reaction, one reactant is oxidized (loses electrons) while another is reduced (gains electrons), resulting in the conversion of chemical species and the release or absorption of energy.
Nickel-metal hydride batteries: Nickel-metal hydride (NiMH) batteries are a type of rechargeable battery that use a hydrogen-absorbing alloy for the negative electrode and nickel oxyhydroxide for the positive electrode. They are a popular alternative to traditional nickel-cadmium batteries, offering higher energy density and improved environmental friendliness.
Alkaline Batteries: Alkaline batteries are a type of electrochemical cell that uses an alkaline electrolyte, typically potassium hydroxide (KOH), instead of the acidic electrolyte found in traditional zinc-carbon batteries. They are a popular choice for powering a wide range of everyday electronic devices due to their reliable performance and long-lasting power.
Manganese Dioxide: Manganese dioxide (MnO2) is a naturally occurring mineral compound composed of manganese and oxygen. It is a dark brown or black solid material that has various applications, particularly in the context of batteries and fuel cells.
Fuel Cells: Fuel cells are electrochemical devices that convert the chemical energy of a fuel, such as hydrogen, directly into electrical energy through a chemical reaction. They serve as an efficient and environmentally-friendly alternative to traditional power generation methods.
Electrolysis: Electrolysis is the process of using electric current to drive a non-spontaneous chemical reaction. It involves the decomposition of chemical compounds by passing an electric current through them, resulting in the separation of their constituent elements. This process is fundamental to various applications, including the production of metals, the treatment of water, and the recharging of batteries.
Faraday's Laws of Electrolysis: Faraday's laws of electrolysis are two fundamental principles that describe the quantitative relationship between the amount of a substance produced at an electrode during electrolysis and the amount of electric charge passed through the electrolytic cell. These laws are crucial in understanding the mechanisms and applications of batteries and fuel cells.
Energy Density: Energy density is a measure of the amount of energy stored per unit of volume or mass in a given substance or material. It is an important consideration in the context of energy storage and conversion technologies, such as batteries and fuel cells, as it directly impacts the efficiency, portability, and practicality of these systems.
Galvanization: Galvanization is the process of applying a protective zinc coating to metal surfaces, typically iron or steel, to prevent corrosion and rust. This technique is widely used in various industries, including construction, automotive, and infrastructure, to enhance the durability and longevity of metal components.
Power Density: Power density is a measure of the amount of power generated or consumed per unit of volume or area. It is a crucial parameter in the design and performance of various energy systems, including batteries and fuel cells.
Ampere-hour: The ampere-hour (Ah) is a unit of electrical charge that measures the amount of electric current flowing for a specific duration of time. It is commonly used to quantify the capacity and energy storage capabilities of batteries and fuel cells.
Oxidation-reduction: Oxidation-reduction, also known as redox, is a fundamental chemical process that involves the transfer of electrons between two substances. It is a key concept in understanding the behavior of batteries, fuel cells, and other electrochemical systems.
Cathode: A cathode is an electrode where reduction occurs during an electrochemical reaction. It plays a crucial role in various processes such as galvanic cells, where it attracts cations from the electrolyte, facilitating the flow of electric current. Understanding the function of the cathode is essential for grasping concepts like electrode potentials and energy transformations in electrochemical cells.
Electromotive Force: Electromotive force (EMF) is the electrical energy produced per unit charge by a source, such as a battery or a fuel cell, when it is not supplying current. It reflects the ability of the source to drive electric charge through a circuit, representing the maximum potential difference that can be achieved. EMF is crucial for understanding how batteries and fuel cells generate and supply electrical energy, making it fundamental in evaluating their performance and efficiency.
Polyethylene: Polyethylene is a widely used synthetic polymer made from the polymerization of ethylene monomers. This versatile plastic is known for its durability, chemical resistance, and lightweight nature, making it essential in various applications including packaging, containers, and insulation. Its electrical insulating properties also make it relevant in the context of energy storage technologies.