What Are Electrochemical Devices?

Electrochemical devices are components and systems that convert between chemical energy and electrical energy, or that exploit electrochemical reactions for sensing, synthesis, or material processing. They share a common architecture: two electrodes separated by an electrolyte through which ions migrate while electrons travel through an external circuit. The electrochemical reactions at each electrode surface involve charge transfer coupled to changes in chemical composition, oxidation state, or material structure. This category includes energy storage devices such as batteries and supercapacitors, energy conversion devices such as fuel cells, and measurement instruments such as amperometric sensors. Electrochemical devices are central to the transition toward electrified transportation, grid energy storage, and distributed power systems.

Batteries and Battery Management

A battery consists of one or more electrochemical cells, each containing a negative electrode (anode during discharge), a positive electrode (cathode during discharge), and an electrolyte. During discharge, oxidation at the anode releases electrons that flow through the external circuit, while reduction at the cathode consumes them; the process reverses during charging in secondary (rechargeable) batteries. Lithium-ion batteries, which use intercalation electrodes and a lithium-salt electrolyte, dominate portable electronics and electric vehicle applications because of their high specific energy (up to approximately 300 Wh/kg at the cell level) and cycle life. IEEE Standard 1725 on rechargeable batteries for cellular telephones and the companion IEEE 1625 for laptop batteries define safety, design, and testing requirements. Battery management systems (BMS) monitor cell voltages, currents, and temperatures in real time, enforce charge and discharge limits, perform cell balancing, and estimate state of charge (SOC) and state of health (SOH) using algorithms based on equivalent circuit models or electrochemical models. Accurate SOH estimation is essential for predicting remaining useful life in stationary storage and vehicle applications.

Fuel Cells

A fuel cell is an electrochemical device that converts the chemical energy of a continuously supplied fuel, typically hydrogen, into electricity through an electrochemical reaction rather than combustion. In a proton exchange membrane fuel cell (PEMFC), hydrogen is oxidized at the anode to produce protons and electrons; protons cross the polymer membrane to the cathode, where they combine with oxygen and the electrons returning from the external circuit to produce water. PEMFCs operate at 60 to 80 degrees Celsius, respond rapidly to load changes, and are suited to light-duty vehicle and backup power applications. Solid oxide fuel cells (SOFCs) operate at 700 to 1,000 degrees Celsius, tolerate a wider range of fuels including natural gas and syngas, and achieve high electrical efficiency, making them attractive for stationary combined heat and power systems. The U.S. Department of Energy's Fuel Cell Technologies Office publishes performance targets and roadmaps that define efficiency, durability, and cost benchmarks for each fuel cell type.

Supercapacitors and Amperometric Sensors

Supercapacitors (also called electrochemical double-layer capacitors or ultracapacitors) store charge electrostatically at the interface between a high-surface-area carbon electrode and an electrolyte, rather than through faradaic reactions. They offer specific power (kilowatts per kilogram) far exceeding batteries and cycle lives exceeding one million charge-discharge cycles, but their specific energy (typically 5 to 15 Wh/kg) is lower. Hybrid supercapacitors combine a battery-type faradaic electrode with a capacitive electrode to achieve intermediate specific energy and power. Amperometric sensors measure the current produced by an electrochemical reaction at a working electrode held at a fixed potential relative to a reference electrode; the current is proportional to the concentration of the analyte at the electrode surface. Glucose biosensors, the most widely deployed amperometric sensor, use enzyme-catalyzed oxidation of glucose at a working electrode to produce a current read by a handheld meter. NIST Standard Reference Material 965b provides certified glucose reference solutions used to calibrate clinical glucose analyzers.

Applications

Electrochemical devices have applications in:

• Electric vehicle propulsion, where lithium-ion battery packs provide stored energy and regenerative braking recovery
• Grid energy storage, using large-format lithium-ion, flow battery, or supercapacitor systems to balance renewable generation variability
• Backup and uninterruptible power supply, where valve-regulated lead-acid and lithium-ion batteries maintain power during grid outages
• Hydrogen fuel cell vehicles and stationary power, converting hydrogen to electricity with water as the only exhaust product
• Clinical diagnostics, where amperometric biosensors measure blood glucose, lactate, and other analytes at the point of care
• Industrial electrochemical synthesis, using controlled electrochemical reactions to produce chlorine, aluminum, and specialty chemicals