Hydrogen by electrolysis

Making hydrogen fuel by splitting water with electricity.

China leads hydrogen by electrolysis research, with 53.0% of the 10% most cited papers published 2021–2025; South Korea is second with 4.7%.

FirstChina53.0%

SecondSouth Korea4.7%

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

Highlight a country

Standings

1CNChina53.0%2KRSouth Korea4.7%3USUnited States4.3%4AUAustralia3.8%5DEGermany3.7%6INIndia2.5%7GBUnited Kingdom2.3%8SASaudi Arabia1.7%9CACanada1.5%10SGSingapore1.4%

Share of the 10% most cited papers, 2021–2025; 1,564 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
Acidic oxygen-evolution catalysts for PEM electrolysis (Ir, Ru)	236	CNChina68.2%	USUnited States4.4%	DEGermany4.1%
Techno-economics, hydrogen economy and policy reviews	213	DEGermany8.2%	CNChina8.0%	USUnited States7.9%
Bifunctional catalysts for overall water splitting	187	CNChina71.6%	KRSouth Korea11.0%	INIndia4.9%
Alkaline oxygen-evolution catalysts (Ni, Co, Fe)	180	CNChina62.2%	KRSouth Korea4.8%	USUnited States4.6%
Hydrogen-evolution catalysts	180	CNChina67.1%	USUnited States4.2%	AUAustralia3.3%
Renewable-powered hydrogen systems and energy-system optimisation	136	CNChina19.7%	GBUnited Kingdom6.3%	ITItaly5.2%
Hybrid electrolysis (hydrazine or organic oxidation)	127	CNChina75.9%	KRSouth Korea5.6%	USUnited States4.3%
Seawater electrolysis	112	CNChina70.1%	AUAustralia7.3%	DEGermany2.4%
Electrolyser technologies and stacks (PEM, alkaline, solid oxide)	75	CNChina20.6%	DEGermany7.8%	USUnited States7.2%

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 46.1%57.9%+11.8 pts

KRSouth Korea 6.6%3.3%−3.3 pts

USUnited States 4.4%4.3%−0.1 pts

AUAustralia 4.4%3.4%−1.1 pts

DEGermany 5.8%2.2%−3.5 pts

INIndia 1.9%2.9%+1.1 pts

GBUnited Kingdom 2.5%2.2%−0.3 pts

SASaudi Arabia 1.1%2.1%+1.0 pts

Share of the 10% most cited papers: 648 papers in 2021–2023, 916 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 (5,006), 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.

CNChina57.0%of 2026 papers have an author here
KRSouth Korea7.8%of 2026 papers have an author here
INIndia7.2%of 2026 papers have an author here
USUnited States4.9%of 2026 papers have an author here
SASaudi Arabia4.2%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 76.6%50.2%+26.4

USUnited States 10.4%6.7%+3.7

KRSouth Korea 10.9%8.2%+2.7

AUAustralia 8.5%4.2%+4.3

DEGermany 12.3%5.5%+6.8

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

1CNChinese Academy of SciencesGovernment lab1.4%
2CNQingdao University of Science and Technology1.4%
3CNUniversity of Science and Technology of China1.3%
4CNHarbin Institute of Technology1.2%
5CNNankai University1.2%
6CNZhejiang University1.0%
7CNTianjin University0.9%
8CNTsinghua University0.9%
9SGNanyang Technological University0.8%
10CNBeijing University of Chemical Technology0.8%

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

Who does the work

Sector	All	CN	KR	US
Universities	82.1%	84.0%	88.5%	80.0%
Research facilities	13.2%	10.6%	9.9%	14.4%
Government labs	2.8%	3.9%	0%	0.8%
Companies	1.1%	1.0%	1.6%	2.0%

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

Across borders

42.5% of the top 10% have authors in more than one country.

AUCNAustralia with China97
CNUSChina with United States68
CNHKChina with Hong Kong61
CNTWChina with Taiwan50
CNGBChina with United Kingdom44

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.

Hydrogen energy systems: A critical review of technologies, applications, trends and challenges
Renewable and Sustainable Energy Reviews, 2021FR
2,321citations
Clean and Affordable Hydrogen Fuel from Alkaline Water Splitting: Past, Recent Progress, and Future Prospects
Advanced Materials, 2021CN
1,946citations
Hydrogen production from water electrolysis: role of catalysts
Nano Convergence, 2021US
1,516citations
A review on hydrogen production and utilization: Challenges and opportunities
International Journal of Hydrogen Energy, 2021CA
1,516citations
An overview of water electrolysis technologies for green hydrogen production
Energy Reports, 2022KR
1,499citations

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.

"water electrolysis" OR electrolyzer OR electrolyser OR "green hydrogen"

and its main topic in OpenAlex is one of: Electrocatalysts for Energy Conversion; Hybrid Renewable Energy Systems; Advancements in Solid Oxide Fuel Cells; Integrated Energy Systems Optimization. The topic check removes papers that only mention the technology.

Papers matched, 2021–2025: 15,680
In the top 10%: 1,564
In the top 1%: 159
Countries with credit: 83
Credit with no known country: 2.3%

Every one of the 1,835 most cited papers was checked for relevance; 43 were left out as not about hydrogen by electrolysis

The most cited of those left out:

Towards underground hydrogen storage: A review of barriers432 citations
Ammonia as a hydrogen energy carrier293 citations
A review of hydrogen utilization in power generation and transportation sectors: Achievements and future challenges288 citations
Tuning Two‐Electron Oxygen‐Reduction Pathways for H2O2 Electrosynthesis via Engineering Atomically Dispersed Single Metal Site Catalysts235 citations
The determinants of renewable energy sources for the fueling of green and sustainable economy220 citations
Blue hydrogen: Current status and future technologies218 citations
Energy, environment, and economic analyses on a novel hydrogen production method by electrified steam methane reforming with renewable energy accommodation201 citations
Vacancy Optimized Coordination on Nickel Oxide for Selective Electrocatalytic Oxidation of Glycerol197 citations
Why turquoise hydrogen will Be a game changer for the energy transition195 citations
Energy demand and supply planning of China through 2060190 citations
Orange hydrogen is the new green187 citations
Advanced Oxygen Electrocatalyst for Air-Breathing Electrode in Zn-Air Batteries175 citations

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

Read the method