Name: primary, rechargeable batteries and fuel cells
Uploaded: 2020-09-24T15:06:52.000Z
Duration: 3 min 12 s
Channel: JoVE

K12 Standards

Pennsylvania State Academic Standards

9-12

Physical Science

Forces and Interactions

3.2.9-12.M

Batteries and Fuel Cells

As baterias são células voltaicas utilizadas como fontes elétricas portáteis. Estão categorizadas em baterias primárias ou não recarregáveis e baterias secundárias ou recarregáveis. A pilha primária comum é a célula seca.Contém uma caixa de zinco como anodo e um cátodo de grafite imerso uma pasta eletrolítica húmida e ácida de óxido de manganês e cloreto de amoníaco. O zinco oxida-se em cloreto de zinco, e o óxido de manganês reduz-se a óxido de manganês sólido gerando um potencial de 1, 5 volts. Quando operados, os elétrodos ficam gastos, tornando as células secas em baterias de utilização única.As baterias alcalinas são semelhantes mas utilizam um eletrólito alcalino prolongando a sua vida útil. As baterias de chumbo-ácido são baterias secundárias predominantemente utilizadas em automóveis. Estas têm tipicamente seis células eletroquímicas ligadas em série, gerando um potencial total de 12 volts.Cada célula tem um anodo de chumbo e um cátodo de óxido de chumbo imerso em ácido sulfúrico. Durante a descarga, as reações redox depositam sulfato de chumbo sólido em ambos os elétrodos, que são convertidos novamente durante o recarregamento utilizando uma fonte de energia externa. As baterias recarregáveis de níquel-cádmio contêm um cátodo de oxidróxido de níquel, um anodo de cádmio, e um eletrólito de hidróxido de potássio.Quando operado, o anodo oxida em hidróxido de cádmio sólido, e o o cátodo reduz-se a hidróxido de níquel sólido, gerando um potencial celular de 1, 3 volts. No entanto, a toxicidade do cádmio leva à substituição de bateria de níquel-hidreto metálico amigas do ambiente. Aqui, o catódico permanece o mesmo, mas o anodo é uma liga absorvente de hidrogénio.A reação anódica envolve a formação de água a partir de hidrogénio. As baterias de íons de lítio são as as mais recentes baterias secundárias. O lítio metálico leve torna estas baterias portáteis com alta densidade energética.Uma bateria de íons de lítio contém um anodo lítico de grafite e um cátodo de óxido de lítio e metal de transição. Quando carregado, o metal de transição fica oxidado, enquanto os íons de lítio são incorporados entre as camadas de grafite anódica. Após a descarga, os íons de lítio fluem desde o anodo até ao cátodo gerando um potencial de 3, 7 volts.Finalmente, as células combustíveis são células voltaicas que requerem um abastecimento externo contínuo de reagentes redox para a produção de energia. Uma típica célula de hidrogénio combustível utiliza hidrogénio e oxigénio do ar para gerar uma corrente durante a emissão de água. Os elétrodos de grafite contêm catalisadores à base de platina para acelerar a reação redox.

baterias e células de combustível

Uma bateria é uma célula galvânica que é utilizada como fonte de energia elétrica para aplicações específicas. As baterias modernas existem em várias formas para acomodar várias aplicações, desde as pequenas pilhas tipo botão, tais como as que alimentam os relógios de pulso até baterias muito grandes utilizadas para fornecer energia de reserva às redes elétricas municipais. Algumas baterias foram concebidas para aplicações de utilização única e não podem ser recarregadas (células primárias), enquanto que outras se baseiam em reações de células convenientemente reversíveis que permitem o recarregamento através de uma fonte de alimentação externa (células secundárias).
Baterias de Utilização Única (Primárias)
Uma pilha seca é uma bateria primária comum que usa zinco tanto como recipiente como ânodo (terminal “–”) e uma haste de grafite como cátodo (terminal “+”). A lata de Zn é enchida com uma pasta eletrolítica contendo óxido de manganês(IV), cloreto de zinco(II), cloreto de amónio, e água. Uma haste de grafite está imersa na pasta de eletrólitos para completar a pilha. A reação espontânea da pilha envolve:
<img alt="Eq1" src="/files/ftp_upload/11439/11439_Equation_1.png" style="text-align: center; height: 168px;" />
A voltagem (potencial celular) de uma pilha seca é de aproximadamente 1,5 V (Ecell ~ 1,5 V). As pilhas secas estão disponíveis em vários tamanhos (por exemplo, D, C, AA, AAA). Todos os tamanhos de pilhas secas compreendem os mesmos componentes e apresentam a mesma voltagem, mas pilhas maiores contêm maiores quantidades de reagentes redox e, portanto, são capazes de transferir quantidades de carga proporcionalmente maiores. Tal como outras células galvânicas, as pilhas secas podem ser ligadas em série para produzir baterias com maiores saídas de voltagem, se necessário. 
As pilhas alcalinas foram concebidas em torno dos mesmos pares redox da pilha seca. Como o seu nome sugere, estes tipos de pilhas utilizam eletrólitos alcalinos, muitas vezes hidróxido de potássio. As reações são
<img alt="Eq2" src="/files/ftp_upload/11439/11439_Equation_2.png" style="text-align: center; height: 130px;" />
Uma pilha alcalina pode fornecer cerca de três a cinco vezes a energia de uma pilha seca de tamanho semelhante (Ecell  = +1,43 V). As pilhas alcalinas têm tendência a verter hidróxido de potássio, pelo que devem ser removidas dos dispositivos para armazenamento a longo prazo. Embora algumas pilhas alcalinas sejam recarregáveis, a maioria não é.
Baterias Recarregáveis (Secundárias)
As baterias de níquel-cádmio, ou NiCd, são constituídas por um cátodo revestido por níquel, um ânodo revestido por cádmio, e um elétrodo de hidróxido de potássio. As placas positivas e negativas, que são impedidas de entrar em curto-circuito pelo separador, são enroladas e colocadas na caixa. Este design permite que a bateria NiCd forneça muito mais corrente do que uma pilha alcalina de tamanho semelhante. As reações são
<img alt="Eq3" src="/files/ftp_upload/11439/11439_Equation_3.png" style="text-align: center; height: 130px;" />
Quando devidamente tratada, uma bateria NiCd pode ser recarregada cerca de 1000 vezes (Ecell ~ 1,3 V). O cádmio é um metal pesado tóxico, pelo que as baterias NiCd nunca devem ser rompidas ou incineradas, devendo ser eliminadas em conformidade com as diretivas aplicáveis relativas aos resíduos tóxicos.
As baterias de ião de lítio estão entre as pilhas recarregáveis mais populares e são utilizadas em muitos dispositivos eletrónicos portáteis. As reações são
<img alt="Eq4" src="/files/ftp_upload/11439/11439_Equation_4.png" style="text-align: center; height: 130px;" />
A estequiometria variável da reação da célula leva à variação das voltagens da célula, mas para condições típicas, x geralmente não é mais que 0,5, e a voltagem da célula é de aproximadamente 3,7 V (Ecell ~ 3,7). As baterias de lítio são populares porque podem fornecer uma grande quantidade de corrente, são mais leves do que as baterias comparáveis de outros tipos, produzem uma voltagem quase constante à medida que são descarregadas, e apenas perdem lentamente a carga quando armazenadas.
A bateria de chumbo-ácido é também um tipo de bateria secundária normalmente utilizada em automóveis. É barata e capaz de produzir a corrente elevada requerida por motores de arranque de automóveis. As reações para uma bateria de chumbo-ácido são
<img alt="Eq5" src="/files/ftp_upload/11439/11439_Equation_5.png" style="text-align: center; height: 160px;" />
Cada célula produz 2 V (Ecell ~ 2 V), pelo que seis células são ligadas em série para produzir uma bateria de 12 V. As baterias de chumbo-ácido são pesadas e contêm um eletrólito cáustico líquido, H2SO4 (aq), mas muitas vezes continuam a ser a bateria de eleição devido à sua elevada densidade de corrente. Uma vez que estas baterias contêm uma quantidade significativa de chumbo, devem ser sempre eliminadas correctamente.
Células de Combustível
Uma célula de combustível é uma célula galvânica que utiliza combustíveis tradicionais, mais frequentemente hidrogénio ou metano, que são continuamente alimentados para a célula juntamente com um oxidante. Dentro da célula, o combustível e o oxidante sofrem a mesma química redox de quando são queimados, mas através de um eletroquímico catalisado que é significativamente mais eficiente. Por exemplo, uma célula de combustível de hidrogénio típica utiliza elétrodos de grafite embebidos em catalisadores à base de platina para acelerar as duas reações de semi-célula:
<img alt="Eq6" src="/files/ftp_upload/11439/11439_Equation_6.png" style="text-align: center; height: 130px;" />
Estes tipos de células de combustível produzem geralmente voltagens de aproximadamente 1,23 V (Ecell ~ 1,23 V). Em comparação com um motor de combustão interna, a eficiência energética de uma célula de combustível que utiliza a mesma reação redox é normalmente mais do dobro (~20%–25% para um motor versus ~50%–75% para uma célula de combustível). Células de combustível de hidrogénio são comumente usadas em missões espaciais extensas, e foram desenvolvidos protótipos para veículos pessoais.
Este texto é adaptado de <a href="https://openstax.org/books/chemistry-2e/pages/17-5-batteries-and-fuel-cells">Openstax, Chemistry 2e, Section 17.5: Batteries, and Fuel Cells.</a>

Baterias e Células de Combustível

Uma bateria é uma célula galvânica usada como fonte de energia elétrica para aplicações específicas. As baterias modernas existem em uma infinidade de formas para ...

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primary, rechargeable batteries and fuel cells

Batteries and fuel cells are galvanic cells that supply electrical power for many applications. They range from tiny button batteries in wristwatches to large systems that can provide backup energy to municipal power grids. Some are primary cells, which are single-use and cannot be recharged. Others are secondary cells, which use reversible reactions and can be charged again by an external power source.

A common primary battery is the dry cell. It uses zinc as both the container and the anode, or negative terminal, and a graphite rod as the cathode, or positive terminal. The zinc can holds an electrolyte paste with manganese(IV) oxide, zinc(II) chloride, ammonium chloride, and water. A dry cell has a voltage of about 1.5 V. It comes in sizes such as D, C, AA, and AAA. These sizes use the same parts and the same voltage, but larger cells contain more reactants and can transfer more charge. Dry cells can also be connected in series to increase voltage.

Alkaline batteries use the same redox couples as dry cells, but they use an alkaline electrolyte, often potassium hydroxide. They can deliver about three to five times the energy of a dry cell of similar size and have a cell potential of about 1.43 V. These batteries can leak potassium hydroxide, so they should be removed from devices during long-term storage. Some alkaline batteries are rechargeable, but most are not.

Rechargeable batteries include nickel-cadmium, or NiCd, batteries, lithium-ion batteries, and lead-acid batteries. A NiCd battery has a nickel-plated cathode, a cadmium-plated anode, and a potassium hydroxide electrode. The positive and negative plates are rolled together with a separator to keep them from shorting. This design lets a NiCd cell deliver much more current than a similar-sized alkaline battery. When treated properly, it can be recharged about 1000 times, and its cell potential is about 1.3 V. Cadmium is toxic, so NiCd batteries should not be ruptured or burned and must be disposed of as toxic waste.

Lithium-ion batteries are widely used in portable electronic devices. Their reaction has variable stoichiometry, so the voltage can vary, but under typical conditions the cell potential is about 3.7 V. These batteries are popular because they can provide a large amount of current, are lighter than comparable batteries of other types, and keep a nearly constant voltage as they discharge. They also lose charge slowly during storage. Lead-acid batteries are common in automobiles. They are inexpensive and can deliver the high current needed by starter motors. Each cell produces 2 V, so six cells are connected in series to make a 12-V car battery. These batteries are heavy and contain a caustic sulfuric acid electrolyte, and they also contain a significant amount of lead, so they must be disposed of properly.

A fuel cell is also a galvanic cell, but it uses a fuel that is continuously fed into the cell along with an oxidant. The fuel is often hydrogen or methane. Inside the cell, the same redox chemistry that occurs in combustion is carried out by a catalyzed electrochemical process that is much more efficient. A typical hydrogen fuel cell uses graphite electrodes with platinum-based catalysts to speed the half-cell reactions. These fuel cells usually produce about 1.23 V. Compared with an internal combustion engine, a fuel cell using the same redox reaction is typically more than twice as efficient. Hydrogen fuel cells are used on extended space missions, and prototypes for personal vehicles have been developed.

Primary, Rechargeable Batteries and Fuel Cells

primary-rechargeable-batteries-and-fuel-cells

balancing redox equations

Redox Reactions and Half-Reaction Balancing

Redox reactions involve electron transfer and changes in oxidation number. In electrochemistry, these reactions connect chemical changes with electrical energy. They also power technologies such as industrial metal processing and rechargeable batteries used in electric vehicles. Oxidation number is a way to track how an atom's electronic environment changes compared with the pure element, where the oxidation number is zero. For a simple ionic compound, the oxidation number matches the ion...

electromotive force

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Electric current is the flow of electric charge through a conducting medium or a solution. In wires, that charge is carried by electrons. In some solutions, ions can also move and carry charge. When electrons move through a wire, they produce an electric current. This idea connects to redox reactions, where electrons are lost and gained. In the spontaneous reaction between zinc and copper ions, zinc is oxidized to zinc ions. Copper ions are reduced to solid copper. Even so, this direct...

voltaic/galvanic cells

Galvanic Cells and Battery Reactions

Galvanic cells use spontaneous redox reactions to produce electric current. A common example is a disposable AA battery, which powers devices by turning chemical energy into electrical energy. Another example is a copper wire placed in silver nitrate solution, where the solution slowly turns bright blue and a grey solid forms on the wire. In the copper and silver reaction, copper is oxidized and silver ions are reduced. Copper forms cuprous ions, which give the solution its blue color. At the...

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Electrode potentials help predict whether a redox reaction will happen on its own. A redox reaction involves electron transfer. In electrochemistry, the measured value is called cell potential or cell voltage. It shows the energy linked to charge transfer and is measured in volts, where 1 volt equals 1 joule per coulomb. A single half-cell cannot be measured by itself because electron transfer needs both a donor and a receiver. For that reason, scientists measure the difference between two...

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Redox Cell Potential, ΔG°, and K

Redox cell potential connects chemical energy, free energy change, and the equilibrium constant in an electrochemical cell. In these reactions, chemical energy is converted into electrical energy. That link helps predict whether a reaction is spontaneous and how far it may proceed. Thermodynamics is the study of how heat and other forms of energy are related. In an electrochemical cell, cell potential can also reflect oxidizing strength or reducing strength. A similar idea appears in acid-base...

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Cell potential changes when a redox reaction does not run at standard conditions. Standard cell potentials connect with standard free energy change, ΔG°, and the equilibrium constant K, but those relationships only hold at 1 M concentration, 298 K, and 1 atmosphere. A zinc(II) and tin(II) redox cell with E°cell = +0.291 V and ΔG° = −56.2 kJ is spontaneous under those standard conditions. As a cell discharges, the reactant concentration changes and the cell potential steadily drops. Many redox...

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Cell Potential from Concentration Differences

Concentration cells are voltaic cells that use two almost identical half-cells. The half-cells use the same electrode and the same half-reaction. They differ only in the concentration of one redox species, so the cell potential depends on that concentration difference. In a concentration cell, the Nernst equation can be used to find the cell potential. For the zinc example shown, the calculated cell potential is positive. A positive cell potential means the overall reaction is spontaneous. <br...

batteries and fuel cells

Batteries and fuel cells are galvanic cells that supply electrical power for many applications. They range from tiny button batteries in wristwatches to large systems that can provide backup energy to municipal power grids. Some are primary cells, which are single-use and cannot be recharged. Others are secondary cells, which use reversible reactions and can be charged again by an external power source. A common primary battery is the dry cell. It uses zinc as both the container and the anode,...

corrosion

Rusting and Metal Protection

Corrosion is the natural breakdown of metals through electrochemical reactions. It can appear as rust on iron, tarnish on silver, or a blue-green patina on copper. In each case, the metal is oxidized. Some corrosion products can protect the surface, while others keep damaging the metal. Rusting is the harmful type of corrosion seen in iron. It happens when iron is exposed to oxygen and water. A galvanic cell forms on the iron surface, and this drives oxidation at the anodic region and...

electrolysis

Electrolysis in Batteries and Metal Production

Electrolysis uses electrical energy to drive a nonspontaneous redox reaction. In a galvanic cell, a spontaneous redox reaction does electrical work on the surroundings by sending electrons through an external circuit. In electrolysis, an external circuit does work on the redox system by applying a voltage large enough to force the reaction in the opposite direction. This process is used in several real-world settings. Recharging a battery is one example, because an outside power source drives...

key terms and concepts

Explore dry cells, alkaline batteries, NiCd, lithium-ion, and lead-acid batteries, plus how hydrogen fuel cells turn fuel into electricity more efficiently.

Primary, Rechargeable Batteries and Fuel Cells | JoVE K12

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3.2.9-12.L

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Primary, Rechargeable Batteries and Fuel Cells

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