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Principal Energy Uses: Electricity, Transportation

Hydrogen is a versatile energy currency that can be produced from fossil fuels or water and that also occurs naturally in rocks underground. Hydrogen has very low energy density by volume but is extremely energy dense by weight. Although it is currently used primarily as a feedstock for oil refining, chemicals, and fertilizers, hydrogen shows promise as a clean fuel for heavy-duty transportation, steel-making, heating, and energy storage. Hydrogen is often referred to as the “Swiss Army knife of decarbonization”, because it has potential in hard to decarbonize applications; however, it is still nascent and a lot needs to happen (regulatory, tech innovation, infrastructure build-out) before it can contribute to decarbonization.

Today, the vast majority of produced hydrogen is created from fossil fuels, but renewable hydrogen can be created through electrolysis, the process of using electricity to create hydrogen from water. Electrolysis is more expensive than fossil fuel hydrogen and other fuels, but the relative costs are rapidly decreasing due to technological innovation, government subsidies, investment activity, and commercialization.

Geologic hydrogen, hydrogen that occurs naturally in rocks underground, is difficult to detect and has long been overlooked. However, breakthroughs in recent years have generated significant interest and investment in the prospect of geologic hydrogen as an economically viable clean energy source.

Current Status

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Change in Global Pure Hydrogen Demand 

Categories of Hydrogen*

Brown Hydrogen 
Hydrogen produced from coal gasification

Grey Hydrogen 
Hydrogen produced from steam methane reforming, a process which converts natural gas into hydrogen and CO2

Blue Hydrogen  
Hydrogen produced from steam methane reforming, and the CO2 produced is captured and stored

Turquoise Hydrogen  
Hydrogen produced via methane pyrolysis, a process that splits methane, the main component of natural gas, into hydrogen and solid carbon

Yellow Hydrogen
Hydrogen produced from grid electricity through electrolysis

Pink Hydrogen
Hydrogen produced from nuclear energy through electrolysis

Green Hydrogen
Hydrogen produced from renewable electricity through electrolysis

White/Gold Hydrogen
Hydrogen that occurs in natural deposits underground

*All hydrogen is the same. Colors are assigned based on the environmental impact of how the hydrogen was produced. The colors above are listed in order of their environmental impact. (brown is worst; green, and potentially white/gold, are best).

The Future

Potential Significant Markets

  • Steel production
  • Trucks, planes, and ships
  • Long term energy storage
  • Building and industrial heating
  • Clean chemicals

Growth of Investment in Hydrogen (VC)

420% growth in VC investment from 2017-2022 
($500 million in 2017 to $2.6 billion in 2022)


  • High energy density by weight
  • Can be a low to no carbon fuel
  • Strong policy support and subsidies for hydrogen production
  • Can be paired with renewables to produce zero carbon fuels
  • No air emissions when using / burning hydrogen; only byproduct is water
  • Potential for long term energy storage
  • Potential to decarbonize steel production
  • Potential to replace carbon fuels in transportation
  • Most abundant element on the planet
  • Reduces reliance on imports of fuels


  • Very low energy density by volume
  • Expensive to produce from clean energy (electrolysis)
  • Geologic hydrogen is difficult to detect and is not yet economically recoverable, but this is an active area for start-ups and new tech
  • Difficult to transport and distribute (hydrogen is only liquid at very high pressure and low temperature)
  • One of the most fugitive gases in the world due to small atom size
  • Extremely expensive to build necessary infrastructure for hydrogen transportation and storage (e.g., specially sealed pipelines, refueling stations)
  • Safety concerns of hydrogen fires
  • Lack of public awareness/understanding


Updated April 2024

Before You Watch Our Lecture on

We assign videos and readings to our Stanford students as pre-work for each lecture to help contextualize the lecture content. We strongly encourage you to review the Essential videos and readings below before watching our lecture on Hydrogen. Include selections from the Optional and Useful list based on your interests and available time.


  • Hydrogen 101. Student Energy. May 18, 2015. (3 min)
    Quick overview of what hydrogen is and the two main ways we make it (since it’s an energy carrier, not an energy resource, we have to make it).
  • Your Definitive Guide to Understanding Hydrogen. Cipher. February 28, 2024. (1 page)
    A "cheat sheet" for what hydrogen is and why everybody's talking about it now.
  • The Truth About Hydrogen. DW Planet A. February 25, 2022. (12 min)
    Explores the drivers and barriers to hydrogen contributing to a decarbonized future.
  • How Does a Fuel Cell Work?. Naked Science Scrapbook. October 7, 2011. (4 min)
    Simple demonstration on how fuel cells work.

Optional and Useful

Our Lecture on

This is our Stanford University Understand Energy course lecture on hydrogen. We strongly encourage you to watch the full lecture to understand the potential roles of hydrogen in achieving net zero and to be able to put this complex topic into context. For a complete learning experience, we also encourage you to watch / read the Essential videos and readings we assign to our students before watching the lecture.

Xiaolin Zheng

Presented by: Xiaolin Zheng, PhD; Professor, Mechanical Engineering, Energy Science Engineering; Senior Fellow, Precourt Institute for Energy; Professor, by Courtesy, Materials Science and Engineering, Stanford University
Recorded on: November 6, 2023   Duration: 34 minutes

Table of Contents

(Clicking on a timestamp will take you to YouTube.)
00:00 Introduction & Overview of Hydrogen's Roles for Reducing Greenhouse Gas Emissions 
16:08 Hydrogen Production 
25:31 Hydrogen Storage and Transportation 
31:57 Hydrogen Utilization 
33:33 Summary

Lecture slides available upon request.

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