Hydrogen storage and ammonia fuel

Storing hydrogen, and making and burning ammonia as a carbon-free fuel.

China leads hydrogen storage and ammonia fuel research, with 44.5% of the 10% most cited papers published 2021–2025; Saudi Arabia is second with 4.5%.

Added 14 October 2026. Its top papers were checked for relevance by AI, but its keywords and topic list have not yet been reviewed by hand.

FirstChina44.5%

SecondSaudi Arabia4.5%

9.8×lead, by share of the 10% most cited papers, 2021–2025

Highlight a country

Standings

1CNChina44.5%2–3SASaudi Arabia4.5%2–3AUAustralia4.5%4USUnited States4.2%5INIndia4.1%6PKPakistan3.9%7GBUnited Kingdom3.0%8MAMorocco2.5%9–10KRSouth Korea2.2%9–10JPJapan2.1%

Share of the 10% most cited papers, 2021–2025; 957 papers. Source: OpenAlex, pulled 18 October 2026. Method

Year by year

China

Everyone else, on a larger scale

Share of the 10% most cited papers published in each year. Source: OpenAlex, pulled 18 October 2026. Method

Inside the field

Always the top 10%Pilot

Each paper sorted into one sub-area by an AI model reading its title and abstract, then credited as usual. On 200 hand-labelled papers it chose the same sub-area, or a defensible second, 92% of the time.

Sub-area	Papers	First	Second	Third
Metal hydrides and porous materials for solid-state storage	379	CNChina39.7%	PKPakistan9.4%	MAMorocco5.4%
Nitrate and nitrite reduction to ammonia	131	CNChina77.9%	HKHong Kong6.9%	INIndia2.1%
Compressed, liquid and underground storage, tanks and pipelines	130	CNChina14.1%	AUAustralia13.6%	GBUnited Kingdom11.7%
Ammonia combustion in engines and turbines	90	CNChina56.2%	SASaudi Arabia7.0%	INIndia5.5%
Electrochemical nitrogen reduction to ammonia	68	CNChina60.3%	DKDenmark8.7%	AUAustralia7.6%
Systems, economics and supply chains	39	CNChina17.9%	CACanada8.0%	AUAustralia7.7%
Thermocatalytic ammonia synthesis (Haber-Bosch and successors)	31	CNChina35.8%	DKDenmark13.3%	JPJapan13.2%
Photocatalytic and plasma nitrogen fixation	25	CNChina78.1%	GBUnited Kingdom6.0%	USUnited States4.2%
Liquid organic hydrogen carriers and chemical storage	25	CNChina41.0%	DEGermany7.9%	KRSouth Korea7.2%
Ammonia cracking and direct ammonia fuel cells	17	CNChina54.4%	KRSouth Korea15.0%	SASaudi Arabia10.3%

Share of each sub-area's papers in the top 10%. Source: OpenAlex, pulled 18 October 2026. Method

Earlier and recent

The same top 10%, split into 2021–2023 and 2024–2025.

FallingRising2021–20232024–2025Change

CNChina 38.7%49.2%+10.6 pts

SASaudi Arabia 3.9%5.1%+1.2 pts

AUAustralia 6.4%3.0%−3.4 pts

USUnited States 6.0%2.8%−3.3 pts

INIndia 4.8%3.5%−1.3 pts

PKPakistan 3.1%4.6%+1.5 pts

GBUnited Kingdom 4.6%1.6%−3.0 pts

MAMorocco 0.5%4.1%+3.6 pts

Greyed rows rest on fewer than five papers of credit in one period.

Share of the 10% most cited papers: 425 papers in 2021–2023, 532 in 2024–2025. Source: OpenAlex, pulled 18 October 2026. Method

2026 so far: a different count

Not the most cited papers: every 2026 paper matched so far (2,839), and a paper counts in full for each country on it. This year's papers are too new to rank by citations, so these shares cannot be compared with the ones above.

CNChina53.2%of 2026 papers have an author here
SASaudi Arabia8.5%of 2026 papers have an author here
INIndia5.9%of 2026 papers have an author here
USUnited States5.8%of 2026 papers have an author here
KRSouth Korea4.1%of 2026 papers have an author here

Who cites the top papers

How much more often a country's top papers are cited from home than its size predicts. Expected is the country's share of all papers in the field; the bar is the excess, in percentage points. Home citers include authors citing their own earlier work.

HomeExpectedExcess

CNChina 68.1%51.5%+16.6

AUAustralia 11.3%4.7%+6.6

SASaudi Arabia 15.3%5.4%+9.9

USUnited States 17.6%7.9%+9.7

INIndia 17.9%7.6%+10.3

Based on up to 100 of each country's most cited single-country papers in the top 10%. Source: OpenAlex, pulled 18 October 2026. Method

Behind the share

Institutions with the most credit

1SAKing Fahd University of Petroleum and Minerals2.0%
2CNShanghai Jiao Tong University1.7%
3CNChongqing University1.4%
4PKKhwaja Fareed University of Engineering and Information Technology1.3%
5DKTechnical University of Denmark1.2%
6CNZhejiang University1.1%
7CNYangtze University1.1%
8CNTianjin University1.1%
9CNSouthwest Petroleum University1.0%
10CNJiangsu University of Science and Technology1.0%

Share of the top 10%. Institutions across all 45 technologies

Who does the work

Sector	All	CN	SA	AU
Universities	86.3%	88.2%	99.2%	90.4%
Research facilities	9.7%	8.2%	0.3%	2.0%
Government labs	2.4%	2.5%	0%	7.4%
Companies	0.9%	0.9%	0.6%	0%

Share of credit by type of institution, overall and for the three leading countries.

Across borders

37.5% of the top 10% have authors in more than one country.

PKSAPakistan with Saudi Arabia40
AUCNAustralia with China32
CNUSChina with United States30
CNGBChina with United Kingdom27
CNDEChina with Germany25

Most frequent pairings, by number of shared papers.

The papers behind the numbers

The five most cited papers this definition catches. If one looks out of place, the definition needs work.

Electrochemical ammonia synthesis via nitrate reduction on Fe single atom catalyst
Nature Communications, 2021CAUS
1,519citations
Hydrogen storage methods: Review and current status
Renewable and Sustainable Energy Reviews, 2022OMPK
1,278citations
A study on hydrogen, the clean energy of the future: Hydrogen storage methods
Journal of Energy Storage, 2021TR
1,173citations
Enabling large-scale hydrogen storage in porous media – the scientific challenges
Energy & Environmental Science, 2021DEESGBNL
1,089citations
A review on ammonia, ammonia-hydrogen and ammonia-methane fuels
Renewable and Sustainable Energy Reviews, 2021CN
1,032citations

How this technology is defined

A paper counts if its title or abstract matches the search below. Articles in core journals and proceedings only; retracted papers are excluded.

"hydrogen storage" OR "ammonia synthesis" OR "ammonia fuel" OR "ammonia combustion" OR "ammonia cracking" OR "green ammonia"

and its main topic in OpenAlex is one of: Hydrogen Storage and Materials; Ammonia Synthesis and Nitrogen Reduction; Advanced Combustion Engine Technologies; Combustion and flame dynamics; Metal-Organic Frameworks: Synthesis and Applications; Spacecraft and Cryogenic Technologies; CO2 Sequestration and Geologic Interactions. The topic check removes papers that only mention the technology.

Papers matched, 2021–2025: 9,550
In the top 10%: 957
In the top 1%: 98
Countries with credit: 68
Credit with no known country: 2.6%

Every one of the 1,211 most cited papers was checked for relevance; 4 were left out as not about hydrogen storage and ammonia fuel

The most cited of those left out:

Achieving High Performance Metal–Organic Framework Materials through Pore Engineering353 citations
Design and Advanced Manufacturing of NU‐1000 Metal–Organic Frameworks with Future Perspectives for Environmental and Renewable Energy Applications147 citations
Innovative lignin-based MOFs and COFs for biomedicine, energy storage, and environmental remediation55 citations
Exploring novel characteristics of GaBaX3 (X= F, Cl, Br, I, H) for energy harvesting applications: A DFT-based analysis22 citations

Definition version 0.5, pilot. It is a plain text file: copy it, change it, rerun it.

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