Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an outcome of a particular chemical change, or vice versa. These reactions involve electrons moving via an electronically-conducting phase between electrodes separated by an ionically conducting and electronically insulating electrolyte.
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit. Electrodes are essential parts of batteries that can consist of a variety of materials depending on the type of battery.
An electrochemical cell is a device that generates electrical energy from chemical reactions. Electrical energy can also be applied to these cells to cause chemical reactions to occur. Electrochemical cells which generate an electric current are called voltaic or galvanic cells and those that generate chemical reactions, via electrolysis for example, are called electrolytic cells.
A lithium-ion or Li-ion battery is a type of rechargeable battery which uses the reversible reduction of lithium ions to store energy. The negative electrode of a conventional lithium-ion cell is typically graphite, a form of carbon. This negative electrode is sometimes called the anode as it acts as an anode during discharge. The positive electrode is typically a metal oxide; the positive electrode is sometimes called the cathode as it acts a cathode during discharge. Positive and negative electrodes remain positive and negative in normal use whether charging or discharging and are therefore clearer terms to use than anode and cathode which are reversed during charging.
A galvanic cell or voltaic cell, named after the scientists Luigi Galvani and Alessandro Volta, respectively, is an electrochemical cell in which an electric current is generated from spontaneous Oxidation-Reduction reactions. A common apparatus generally consists of two different metals, each immersed in separate beakers containing their respective metal ions in solution that are connected by a salt bridge or separated by a porous membrane.
In electrochemistry, standard electrode potential, or , is a measure of the reducing power of any element or compound. The IUPAC "Gold Book" defines it as: "the value of the standard emf of a cell in which molecular hydrogen under standard pressure is oxidized to solvated protons at the left-hand electrode".
In electrochemistry, a half-cell is a structure that contains a conductive electrode and a surrounding conductive electrolyte separated by a naturally occurring Helmholtz double layer. Chemical reactions within this layer momentarily pump electric charges between the electrode and the electrolyte, resulting in a potential difference between the electrode and the electrolyte. The typical anode reaction involves a metal atom in the electrode being dissolved and transported as a positive ion across the double layer, causing the electrolyte to acquire a net positive charge while the electrode acquires a net negative charge. The growing potential difference creates an intense electric field within the double layer, and the potential rises in value until the field halts the net charge-pumping reactions. This self-limiting action occurs almost instantly in an isolated half-cell; in applications two dissimilar half-cells are appropriately connected to constitute a Galvanic cell.
A regenerative fuel cell or reverse fuel cell (RFC) is a fuel cell run in reverse mode, which consumes electricity and chemical B to produce chemical A. By definition, the process of any fuel cell could be reversed. However, a given device is usually optimized for operating in one mode and may not be built in such a way that it can be operated backwards. Standard fuel cells operated backwards generally do not make very efficient systems unless they are purpose-built to do so as with high-pressure electrolysers, regenerative fuel cells, solid-oxide electrolyser cells and unitized regenerative fuel cells.
A solid oxide fuel cell is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. Fuel cells are characterized by their electrolyte material; the SOFC has a solid oxide or ceramic electrolyte.
In electrochemistry, overpotential is the potential difference (voltage) between a half-reaction's thermodynamically-determined reduction potential and the potential at which the redox event is experimentally observed. The term is directly related to a cell's voltage efficiency. In an electrolytic cell the existence of overpotential implies that the cell requires more energy than thermodynamically expected to drive a reaction. In a galvanic cell the existence of overpotential means less energy is recovered than thermodynamics predicts. In each case the extra/missing energy is lost as heat. The quantity of overpotential is specific to each cell design and varies across cells and operational conditions, even for the same reaction. Overpotential is experimentally determined by measuring the potential at which a given current density is achieved.
In electrochemistry, electrosynthesis is the synthesis of chemical compounds in an electrochemical cell. Compared to ordinary redox reactions, electrosynthesis sometimes offers improved selectivity and yields. Electrosynthesis is actively studied as a science and also has industrial applications. Electrooxidation has potential for wastewater treatment as well.
Lithium iron phosphate or lithium ferro-phosphate (LFP) is an inorganic compound with the formula LiFePO
4. It is a gray, red-grey, brown or black solid that is insoluble in water. The material has attracted attention as a component of lithium iron phosphate batteries, a type of Li-ion battery. This battery chemistry is targeted for use in power tools, electric vehicles, solar energy installations and more recently large grid-scale energy storage.
The lithium–air battery (Li–air) is a metal–air electrochemical cell or battery chemistry that uses oxidation of lithium at the anode and reduction of oxygen at the cathode to induce a current flow.
The sodium-ion battery (NIB or SIB) is a type of rechargeable battery that uses sodium ions (Na+) as its charge carriers. Its working principle and cell construction in some case are similar to those of lithium-ion battery (LIB) types, but replace lithium with sodium. SIBs received academic and commercial interest in the 2010s and 2020s, largely due to the uneven geographic distribution, high environmental impact and high cost of many of the materials required for lithium-ion batteries. Chief among these are lithium, cobalt, copper and nickel, which are not strictly required for many types of sodium-ion batteries. The largest advantage of sodium-ion batteries is the natural abundance of sodium. Challenges to adoption of SIBs include low energy density and insufficient charge-discharge cycles.
Aluminium-ion batteries are a class of rechargeable battery in which aluminium ions serve as charge carriers. Aluminium can exchange three electrons per ion. This means that insertion of one Al3+ is equivalent to three Li+ ions. Thus, since the ionic radii of Al3+ (0.54 Å) and Li+ (0.76 Å) are similar, significantly higher numbers of electrons and Al3+ ions can be accepted by cathodes with little damage. Al has 50 times (23.5 megawatt-hours m-3) the energy density of Li and is even higher than coal.
Research in lithium-ion batteries has produced many proposed refinements of lithium-ion batteries. Areas of research interest have focused on improving energy density, safety, rate capability, cycle durability, flexibility, and cost.
A triple phase boundary (TPB) is a geometrical class of phase boundary and the location of contact between three different phases. A simple example of a TPB is a coastline where land, air and sea meet to create an energetic location driven by solar, wind and wave energy capable of supporting a high level of biodiversity. This concept is particularly important in the description of electrodes in fuel cells and batteries. For example for fuel cells, the three phases are an ion conductor (electrolyte), an electron conductor, and a virtual "porosity" phase for transporting gaseous or liquid fuel molecules. The electrochemical reactions that fuel cells use to produce electricity occur in the presence of these three phases. Triple phase boundaries are thus the electrochemically active sites within electrodes.
Lithium hybrid organic batteries are an energy storage device that combines lithium with an organic polymer. For example, polyaniline vanadium (V) oxide (PAni/V2O5) can be incorporated into the nitroxide-polymer lithium iron phosphate battery, PTMA/LiFePO4. Together, they improve the lithium ion intercalation capacity, cycle life, electrochemical performances, and conductivity of batteries.
Linda Faye Nazar is a Senior Canada Research Chair in Solid State Materials and Distinguished Research Professor of Chemistry at the University of Waterloo. She develops materials for electrochemical energy storage and conversion. Nazar demonstrated that interwoven composites could be used to improve the energy density of lithium–sulphur batteries. She was awarded the 2019 Chemical Institute of Canada Medal.
Viola Ingrid Birss is a Professor of Chemistry at the University of Calgary. She works on electrochemistry and the development of nanomaterials for sustainable energy and sensing applications. She has demonstrated a metal oxide perovskite that can be used as the air and fuel electrode in solid oxide fuel cells, as well as creating nanoporous carbon scaffolds to be used in batteries and capacitors.
