CHEM1008 - Electrochemistry and Fuel Cells

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Questions and Answers

What is one of the major challenges associated with fuel cells?

Their economic and technological viability is questioned (correct)

They are always powered by fossil fuels

They require constant sunlight to function

They are not environmentally friendly

Which greenhouse gases are primarily responsible for climate change as mentioned?

Ozone and nitrogen dioxide

Hydrogen and oxygen

Carbon dioxide, nitrous oxide, and methane (correct)

Sulfur dioxide and carbon monoxide

What sustainable power source can use solar energy to produce fuel?

Nuclear energy

Wind power

Hydrogen and fuel cells (correct)

Geothermal energy

What is one expected effect of climate change by 2050?

Increase in the number of water-stressed regions Signup and view all the answers

Why might conventional fossil fuel energy sources be replaced?

Their negative environmental impact is significant Signup and view all the answers

Which of the following alternative power sources is mentioned as having high capital costs and geographical dependencies?

Wind energy Signup and view all the answers

What can happen to agricultural patterns due to climate change?

Regional food shortages may occur Signup and view all the answers

What aspect of climate change did the Dept for Environment, Food and Rural Affairs emphasize?

It represents the greatest environmental challenge globally Signup and view all the answers

What is the maximum theoretical efficiency of a heat engine as defined by Carnot's principle?

$rac{T1 - T2}{T1}$ Signup and view all the answers

What primary advantage do fuel cells have over combustion engines in terms of efficiency?

Fuel cells can achieve efficiencies up to about 90%. Signup and view all the answers

In the reaction of hydrogen and oxygen in a fuel cell, what species is produced?

H2O Signup and view all the answers

What does the equation $ ext{∆rG} = -zFEcell$ relate to in the context of a hydrogen fuel cell?

It relates Gibbs energy to the cell voltage and the number of electrons transferred. Signup and view all the answers

What happens to some of the heat produced in a fuel cell?

It is re-used to improve overall efficiency. Signup and view all the answers

What is the process that occurs at the anode of a hydrogen fuel cell?

Oxidation of hydrogen. Signup and view all the answers

Why is the BMW Hydrogen 7 considered a limited production vehicle?

Only 100 units were manufactured. Signup and view all the answers

What limits the efficiency of combustion engines according to the Second Law of Thermodynamics?

The requirement to discard some heat. Signup and view all the answers

Study Notes

Frontiers in Chemistry: CHEM1008 - Electrochemistry and Devices 1 - Fuel Cells

Lecture 1 Learning Outcomes: The lecture aims to:
- Explain the need for new devices to address climate change.
- Introduce alternative power generation methods.
- Discuss why burning fuels isn't always the most effective energy extraction method.
- Explain how fuel cells work and highlight challenges in making them economically and technologically viable.

Climate Change

Key Issue: Climate change is the world's greatest environmental challenge.
Cause: Accumulation of CO2, N2O, and CH4 in the atmosphere prevents heat from escaping, leading to increased temperatures at the surface and lower atmosphere.
DEFRA is the Dept for Environment, Food and Rural Affairs involved with this issue.
Temperature Impact: Nineteen of the twenty warmest years on record have occurred since 2001. 2023 is expected to be the warmest on record.

Climate Change Effects

Water Stress: 1.5 billion people currently live in water-stressed regions, with projections increasing to 7 billion by 2050.
Land Changes: Some regions may become more fertile, while others might become barren.
Economic Impact: Regional food shortages, mass migration, poverty, and malnutrition are anticipated, primarily in developing countries. (Source: IPCC)
Extreme Weather: More frequent and intense heatwaves, floods, storms, wildfires, and droughts are expected.
Health Impacts: Deaths from cold-related diseases may decrease, but associated diseases will change.

Replacing Conventional Fossil Fuels

Fossil Fuel Consumption: A 500 MW power plant could consume 250 tonnes of coal per hour under full load. Ratcliffe-on-Soar power station, a local plant, is one of the last coal-fired power stations in the UK, with a capacity of 2.1 GW.

Alternative Energy Sources

Renewable Sources (Water, Wind, Geothermal): Clean but may demand high capital costs and geographic dependence.
Solar Energy: The Earth receives enough solar energy in 1.5 hours to meet annual energy needs; however, it's essential to effectively store or utilize this energy when the sun isn't shining.
Energy Storage: Energy from solar and wind can be stored in large batteries for later use.
Hydrogen and Fuel Cells: Use solar power to produce hydrogen from water for later fuel use.

Hydrogen Power and Fuel Cells

BMW Hydrogen 7: This limited-production vehicle used a combustion engine that functioned on hydrogen energy from 2005-2007.

Combustion Engine Efficiency Limits

Nature's Limit: Heat engines (like steam and gas turbines) transform heat into usable motion, but some heat must be lost to a cooler environment.
Second Law of Thermodynamics: This law dictates that some heat energy will always be lost during conversion, hence limiting the overall efficiency.

Heat Engines Efficiency

Carnot Efficiency: A basic limit to converting heat into usable work. The conversion rate is (T₁ - T₂)/T_1. Temperatures are always measured in Kelvin.

Fuel Cells vs. Combustion Engines

Fuel Cell Efficiency: Fuel cells can achieve much higher efficiencies (up to 90% in certain instances).
Heat Recovery: Some heat is produced by fuel cells; however, strategies are in place to reuse that heat to effectively make fuel cells highly efficient.

Hydrogen Fuel Cell Chemistry

Net Reaction: The essential chemical reaction in a hydrogen fuel cell is similar (2H₂ + O₂ → 2H₂O) to burning hydrogen in the air .
Gibbs Energy: The useful energy yielded in the process is known as Gibbs energy, as described in CHEM1011 (further details are found in this course)

Hydrogen Fuel Cell Detailed Chemistry

Half-reactions: The H₂ and O₂ reactions require two half reaction processes.
- The anode half-reaction involves hydrogen oxidation.
- The cathode half-reaction involves the reduction of oxygen.

Key Parameter: Power

Electrical Energy: The driving forces are measured through electrical energy, which links to the Gibbs energy of the chemical reaction; AG = -zFEcell

Fuel Cell Performance

Maximum Current & Power: Maximize current and power by using large electrodes and coating them with catalysts (like platinum) to facilitate the necessary reactions. Close electrode placement is essential.

Fuel Cell Electrical Properties

Voltage Drop: The fuel cell's voltage decreases as the current increases. The open-circuit voltage theoretically reaches 1.2V.

Fuel Cell Stacks

Boosting Power Output: Real-world devices typically use interconnected fuel cell stacks to enhance the power output.

Fuel Cell Viability Research

Catalyst Advancement: Chemists concentrate on creating improved, inexpensive fuel cell catalysts, especially those that accelerate oxygen reactions.
Membrane Development: Scientists are focused on creating new, less expensive, and more effective ionically-conducting membranes.
Mass-Transport Improvement: Collaboration with engineers helps create methods to efficiently deliver components needed for quick chemical reaction and prevent energy losses.
Public Awareness: Collaborations with social scientists and industrial partners are crucial to promote hydrogen fuel cells and inform the public about their potential.

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Description

Explore the critical role of fuel cells in addressing climate change. This quiz delves into alternative power generation methods and the importance of developing new technologies to mitigate environmental impacts. Learn about the challenges of making fuel cells a viable energy source.