Anode: Zn (s) Zn 2+ (aq) + 2e - (simplified) Cathode: (simplified reaction) 2 NH 4 + (aq) + 2MnO 2(s) + 2e - Mn 2 O 3(s) + 2 NH 3(aq) + H 2 O Overall reaction: 1981

Anode: Zn (s) Zn 2+ (aq) + 2e - (simplified) Cathode: (simplified reaction) 2 NH 4 + (aq) + 2MnO 2(s) + 2e - Mn 2 O 3(s) + 2 NH 3(aq) + H 2 O Overall reaction: Zn (s) + 2 NH 4 + (aq) + 2MnO 2(s) Zn 2+ (aq) + Mn 2 O 3(s) + 2 NH 3(aq) + H 2 O 1982

Anode: Zn (s) Zn 2+ (aq) + 2e - (simplified) Cathode: (simplified reaction) 2 NH 4 + (aq) + 2MnO 2(s) + 2e - Mn 2 O 3(s) + 2 NH 3(aq) + H 2 O Overall reaction: Zn (s) + 2 NH 4 + (aq) + 2MnO 2(s) Zn 2+ (aq) + Mn 2 O 3(s) + 2 NH 3(aq) + H 2 O The voltage produced is ~ 1.5 V. This cell loses its ability to function rather rapidly under heavy current drain – products don’t diffuse away from the electrode very quickly. Advantage: low price. 1983

In cell notation, the dry cell is: 1984

In cell notation, the dry cell is: Zn(s)|ZnCl 2 (aq),NH 4 Cl(aq)|MnO 2 (s)|Mn 2 O 3 (s)|C 1985

In cell notation, the dry cell is: Zn(s)|ZnCl 2 (aq),NH 4 Cl(aq)|MnO 2 (s)|Mn 2 O 3 (s)|C Note, there is no salt bridge in this cell. 1986

In cell notation, the dry cell is: Zn(s)|ZnCl 2 (aq),NH 4 Cl(aq)|MnO 2 (s)|Mn 2 O 3 (s)|C Note, there is no salt bridge in this cell. A bit more realistic view of the chemistry is: 1987

In cell notation, the dry cell is: Zn(s)|ZnCl 2 (aq),NH 4 Cl(aq)|MnO 2 (s)|Mn 2 O 3 (s)|C Note, there is no salt bridge in this cell. A bit more realistic view of the chemistry is: Anode: 1988

In cell notation, the dry cell is: Zn(s)|ZnCl 2 (aq),NH 4 Cl(aq)|MnO 2 (s)|Mn 2 O 3 (s)|C Note, there is no salt bridge in this cell. A bit more realistic view of the chemistry is: Anode: Zn (s) Zn 2+ (aq) + 2e - followed by 1989

In cell notation, the dry cell is: Zn(s)|ZnCl 2 (aq),NH 4 Cl(aq)|MnO 2 (s)|Mn 2 O 3 (s)|C Note, there is no salt bridge in this cell. A bit more realistic view of the chemistry is: Anode: Zn (s) Zn 2+ (aq) + 2e - followed by Zn 2+ (aq) + 4 NH 3(aq) Zn(NH 3 ) 4 2+ (aq) 1990

In cell notation, the dry cell is: Zn(s)|ZnCl 2 (aq),NH 4 Cl(aq)|MnO 2 (s)|Mn 2 O 3 (s)|C Note, there is no salt bridge in this cell. A bit more realistic view of the chemistry is: Anode: Zn (s) Zn 2+ (aq) + 2e - followed by Zn 2+ (aq) + 4 NH 3(aq) Zn(NH 3 ) 4 2+ (aq) Cathode: 1991

In cell notation, the dry cell is: Zn(s)|ZnCl 2 (aq),NH 4 Cl(aq)|MnO 2 (s)|Mn 2 O 3 (s)|C Note, there is no salt bridge in this cell. A bit more realistic view of the chemistry is: Anode: Zn (s) Zn 2+ (aq) + 2e - followed by Zn 2+ (aq) + 4 NH 3(aq) Zn(NH 3 ) 4 2+ (aq) Cathode: 2MnO 2(s) + H 2 O + e - MnO(OH) (s) + OH - (aq) 1992

In cell notation, the dry cell is: Zn(s)|ZnCl 2 (aq),NH 4 Cl(aq)|MnO 2 (s)|Mn 2 O 3 (s)|C Note, there is no salt bridge in this cell. A bit more realistic view of the chemistry is: Anode: Zn (s) Zn 2+ (aq) + 2e - followed by Zn 2+ (aq) + 4 NH 3(aq) Zn(NH 3 ) 4 2+ (aq) Cathode: 2MnO 2(s) + H 2 O + e - MnO(OH) (s) + OH - (aq) followed by: NH 4 + (aq) + OH - (aq) NH 3(aq) + H 2 O 1993

The mercury battery The mercury battery: 1994

The mercury battery The mercury battery: Applications in electronics industry, cameras, watches, etc. 1995

The mercury battery The mercury battery: Applications in electronics industry, cameras, watches, etc. The battery is contained in a stainless steel cylinder, with a zinc anode (amalgamated with mercury) in contact with a strongly alkaline electrolyte. 1996

The mercury battery The mercury battery: Applications in electronics industry, cameras, watches, etc. The battery is contained in a stainless steel cylinder, with a zinc anode (amalgamated with mercury) in contact with a strongly alkaline electrolyte. Anode: Zn(Hg) (s) + 2 OH - (aq) ZnO (s) + H 2 O (l) + 2e- 1997

The mercury battery The mercury battery: Applications in electronics industry, cameras, watches, etc. The battery is contained in a stainless steel cylinder, with a zinc anode (amalgamated with mercury) in contact with a strongly alkaline electrolyte. Anode: Zn(Hg) (s) + 2 OH - (aq) ZnO (s) + H 2 O (l) + 2e- Cathode: HgO (s) + H 2 O (l) + 2e - Hg (l) + 2 OH - (aq) 1998

The mercury battery The mercury battery: Applications in electronics industry, cameras, watches, etc. The battery is contained in a stainless steel cylinder, with a zinc anode (amalgamated with mercury) in contact with a strongly alkaline electrolyte. Anode: Zn(Hg) (s) + 2 OH - (aq) ZnO (s) + H 2 O (l) + 2e- Cathode: HgO (s) + H 2 O (l) + 2e - Hg (l) + 2 OH - (aq) Overall reaction: Zn(Hg) (s) + HgO (s) ZnO (s) + Hg (l) 1999

The voltage is 1.35 V. The overall cell reaction involves only solid substances. This battery has a longer shelf-life compared to the dry cell. Disadvantage: toxicity of discarded batteries. Environmental impact. 2000

The nickel-cadmium storage cell (nicad battery) 2001

The nickel-cadmium storage cell (nicad battery) This is the type of battery that is used to power electronic calculators, etc. 2002

The nickel-cadmium storage cell (nicad battery) This is the type of battery that is used to power electronic calculators, etc. Anode: Cd (s) + 2 OH - (aq) Cd(OH) 2(s) + 2e- 2003

The nickel-cadmium storage cell (nicad battery) This is the type of battery that is used to power electronic calculators, etc. Anode: Cd (s) + 2 OH - (aq) Cd(OH) 2(s) + 2e- Cathode: NiO (s) + 2H 2 O (l) + 2e - Ni(OH) 2(s) + 2 OH - (aq) 2004

The nickel-cadmium storage cell (nicad battery) This is the type of battery that is used to power electronic calculators, etc. Anode: Cd (s) + 2 OH - (aq) Cd(OH) 2(s) + 2e- Cathode: NiO (s) + 2H 2 O (l) + 2e - Ni(OH) 2(s) + 2 OH - (aq) Overall reaction: Cd (s) + NiO (s) + 2H 2 O (l) Cd(OH) 2(s) + Ni(OH) 2(s) 2005

The nickel-cadmium storage cell (nicad battery) This is the type of battery that is used to power electronic calculators, etc. Anode: Cd (s) + 2 OH - (aq) Cd(OH) 2(s) + 2e- Cathode: NiO (s) + 2H 2 O (l) + 2e - Ni(OH) 2(s) + 2 OH - (aq) Overall reaction: Cd (s) + NiO (s) + 2H 2 O (l) Cd(OH) 2(s) + Ni(OH) 2(s) Disadvantages: Cd is toxic; environmental impact; higher cost. Advantage, can be recharged. 2006

The lead-acid storage battery 2007

The lead-acid storage battery The lead-acid storage battery commonly used in automobiles consists of six identical cells joined together in series. Each cell consists of a lead anode and a cathode made of lead dioxide (lead (IV) oxide). Both the cathode and the anode are immersed in an aqueous solution of sulfuric acid, which acts as the electrolyte. 2008

The lead-acid storage battery The lead-acid storage battery commonly used in automobiles consists of six identical cells joined together in series. Each cell consists of a lead anode and a cathode made of lead dioxide (lead (IV) oxide). Both the cathode and the anode are immersed in an aqueous solution of sulfuric acid, which acts as the electrolyte. Anode: Pb (s) + SO 4 2- (aq) PbSO 4(s) + 2e- 2009

The lead-acid storage battery The lead-acid storage battery commonly used in automobiles consists of six identical cells joined together in series. Each cell consists of a lead anode and a cathode made of lead dioxide (lead (IV) oxide). Both the cathode and the anode are immersed in an aqueous solution of sulfuric acid, which acts as the electrolyte. Anode: Pb (s) + SO 4 2- (aq) PbSO 4(s) + 2e- Cathode: PbO 2(s) + 4H + (aq) + SO 4 2- (aq) + 2e - PbSO 4(s) + 2 H 2 O (l) 2010

The lead-acid storage battery The lead-acid storage battery commonly used in automobiles consists of six identical cells joined together in series. Each cell consists of a lead anode and a cathode made of lead dioxide (lead (IV) oxide). Both the cathode and the anode are immersed in an aqueous solution of sulfuric acid, which acts as the electrolyte. Anode: Pb (s) + SO 4 2- (aq) PbSO 4(s) + 2e- Cathode: PbO 2(s) + 4H + (aq) + SO 4 2- (aq) + 2e - PbSO 4(s) + 2 H 2 O (l) Overall reaction: Pb (s) + 2H 2 SO 4(aq) + PbO 2(s) 2 PbSO 4(s) + 2 H 2 O (l) 2011

Voltage produced is ~ 12 V (2 V from each cell). 2012

Voltage produced is ~ 12 V (2 V from each cell). The battery is rechargeable. 2013

Voltage produced is ~ 12 V (2 V from each cell). The battery is rechargeable. The degree to which the battery has discharged can be checked by measuring the density of the electrolyte. 2014

Voltage produced is ~ 12 V (2 V from each cell). The battery is rechargeable. The degree to which the battery has discharged can be checked by measuring the density of the electrolyte. In cold climates the battery may “go dead”. The cause of the battery’s apparent breakdown is an increase in the viscosity of the electrolyte as the temperature decreases. 2015

Voltage produced is ~ 12 V (2 V from each cell). The battery is rechargeable. The degree to which the battery has discharged can be checked by measuring the density of the electrolyte. In cold climates the battery may “go dead”. The cause of the battery’s apparent breakdown is an increase in the viscosity of the electrolyte as the temperature decreases. For the battery to function properly, the electrolyte must be fully conducting. 2016

Voltage produced is ~ 12 V (2 V from each cell). The battery is rechargeable. The degree to which the battery has discharged can be checked by measuring the density of the electrolyte. In cold climates the battery may “go dead”. The cause of the battery’s apparent breakdown is an increase in the viscosity of the electrolyte as the temperature decreases. For the battery to function properly, the electrolyte must be fully conducting. However, the ions move much more slowly in a viscous medium – leads to lower power output from the battery. 2017

Fuel Cells 2018

Fuel Cells Fossil fuel is a major source of energy. Converting fossil fuel into electrical energy is highly inefficient process. 2019

Fuel Cells Fossil fuel is a major source of energy. Converting fossil fuel into electrical energy is highly inefficient process. e.g. CH 4 + 2O 2 CO H 2 O + heat 2020

Fuel Cells Fossil fuel is a major source of energy. Converting fossil fuel into electrical energy is highly inefficient process. e.g. CH 4 + 2O 2 CO H 2 O + heat To generate electricity, heat produced by the reaction is first used to convert water to steam, which then drives a turbine that drives a generator. 2021

An appreciable amount of energy in the form of heat is lost to the surrounding at each step. Most efficient power plants convert only about 40% of the original chemical energy into electricity. 2022

An appreciable amount of energy in the form of heat is lost to the surrounding at each step. Most efficient power plants convert only about 40% of the original chemical energy into electricity. It would be more desirable to carry out such processes directly by electrochemical means. 2023

An appreciable amount of energy in the form of heat is lost to the surrounding at each step. Most efficient power plants convert only about 40% of the original chemical energy into electricity. It would be more desirable to carry out such processes directly by electrochemical means. This can be accomplished in a fuel cell. A fuel cell consists of an electrolyte solution, such as H 2 SO 4 or NaOH and two inert electrodes. 2024

An appreciable amount of energy in the form of heat is lost to the surrounding at each step. Most efficient power plants convert only about 40% of the original chemical energy into electricity. It would be more desirable to carry out such processes directly by electrochemical means. This can be accomplished in a fuel cell. A fuel cell consists of an electrolyte solution, such as H 2 SO 4 or NaOH and two inert electrodes. H 2 and O 2 are bubbled through the anode and cathode compartments: 2025

Anode: 2H 2(g) + 4OH - (aq) 4H 2 O (l) + 4e- 2026

Anode: 2H 2(g) + 4OH - (aq) 4H 2 O (l) + 4e- Cathode: O 2(g) + 2H 2 O (l) + 4e - 4OH - (aq) 2027

Anode: 2H 2(g) + 4OH - (aq) 4H 2 O (l) + 4e- Cathode: O 2(g) + 2H 2 O (l) + 4e - 4OH - (aq) Overall reaction: 2H 2(g) + O 2(g) 2H 2 O (l) 2028

Anode: 2H 2(g) + 4OH - (aq) 4H 2 O (l) + 4e- Cathode: O 2(g) + 2H 2 O (l) + 4e - 4OH - (aq) Overall reaction: 2H 2(g) + O 2(g) 2H 2 O (l) A potential difference is established between the two electrodes. The overall reaction exactly reverses the electrolysis of H 2 O. 2029

The electrodes serve a double purpose. First, they serve as electrical conductors. 2030

The electrodes serve a double purpose. First, they serve as electrical conductors. Second, the electrodes provide the necessary surfaces for the initial decomposition of the molecules into atomic species, prior to electron transfer. 2031

The electrodes serve a double purpose. First, they serve as electrical conductors. Second, the electrodes provide the necessary surfaces for the initial decomposition of the molecules into atomic species, prior to electron transfer. They are electrocatalysts. Metals such as Pt, Ni, Rh are good electrocatalysts. 2032

2033

In addition to the H 2 – O 2 system, a number of other fuel cells have been developed. 2034

In addition to the H 2 – O 2 system, a number of other fuel cells have been developed. E.g. the propane-dioxygen fuel cell. 2035

In addition to the H 2 – O 2 system, a number of other fuel cells have been developed. E.g. the propane-dioxygen fuel cell. Anode: C 3 H 8(g) + 6H 2 O (l) 3CO 2(g) + 20 H + (aq) + 20e- 2036

In addition to the H 2 – O 2 system, a number of other fuel cells have been developed. E.g. the propane-dioxygen fuel cell. Anode: C 3 H 8(g) + 6H 2 O (l) 3CO 2(g) + 20 H + (aq) + 20e- Cathode: 5O 2(g) + 20 H + (aq) + 20e - 6H 2 O (l) 2037

In addition to the H 2 – O 2 system, a number of other fuel cells have been developed. E.g. the propane-dioxygen fuel cell. Anode: C 3 H 8(g) + 6H 2 O (l) 3CO 2(g) + 20 H + (aq) + 20e- Cathode: 5O 2(g) + 20 H + (aq) + 20e - 6H 2 O (l) Overall reaction: C 3 H 8(g) + 5O 2(g) 3CO 2(g) + 4H 2 O (l) 2038

In addition to the H 2 – O 2 system, a number of other fuel cells have been developed. E.g. the propane-dioxygen fuel cell. Anode: C 3 H 8(g) + 6H 2 O (l) 3CO 2(g) + 20 H + (aq) + 20e- Cathode: 5O 2(g) + 20 H + (aq) + 20e - 6H 2 O (l) Overall reaction: C 3 H 8(g) + 5O 2(g) 3CO 2(g) + 4H 2 O (l) Note the overall reaction is identical to burning propane in dioxygen. 2039

Fuel cells differ from batteries in that the former do not store chemical energy. 2040