Hydrogen produced by electrolysis using renewable electricity. Its lifecycle emissions are not fixed: they depend on the electricity actually used and on the accounting boundary applied, so electrolysis run on dedicated renewables sits among the lowest-carbon routes available while grid-connected electrolysis can carry a materially higher footprint. Green hydrogen costs more than unabated fossil hydrogen today. The IEA's Global Hydrogen Review 2026 identifies China as the one region where renewable hydrogen could reach cost-competitiveness by 2030, and finds low-emissions hydrogen staying more costly than fossil-based hydrogen in most other parts of the world.

Hydrogen produced from natural gas via steam methane reforming (SMR), releasing CO₂ that is not captured. It is the largest single source of the world's hydrogen. Grey hydrogen and coal gasification are the two unabated fossil routes, and hydrogen that is not low-emissions still made up more than 98% of global supply in 2025, when low-emissions production came in under 1% of the total (IEA, Global Hydrogen Review 2026). Grey hydrogen is the economic benchmark green hydrogen has to beat.

Hydrogen produced from fossil fuels (typically SMR) with carbon capture and storage (CCS) to reduce CO₂ emissions. Considered a lower-carbon transition fuel, though debate continues around methane leakage and the permanence of geological CO₂ storage. Blue hydrogen is promoted by gas producers as a near-term bridge to green hydrogen.

A device that uses electricity to split water into hydrogen and oxygen through electrolysis. Electrolyzers are the core technology behind green hydrogen production. The three main types are alkaline, proton exchange membrane (PEM), and solid oxide electrolyzers, each with different efficiency profiles and cost structures.

An electrochemical device that converts hydrogen and oxygen directly into electricity and water, with high efficiency and zero local emissions. Types include PEM (vehicles, portable power), SOFC (solid oxide — stationary power), PAFC (phosphoric acid — stationary), and alkaline. Fuel cells are used in FCEVs (hydrogen cars and trucks), backup power systems, and distributed generation.

The annual fee an ETF charges to cover stated operating costs such as management and administration, expressed as a percentage of assets. Depending on the source it may be quoted gross or net of contractual fee waivers. It does not capture every cost of owning a fund: brokerage commissions, bid-ask spreads, any premium or discount to NAV, and — for futures funds — roll effects are all separate. All else equal, a lower expense ratio means less annual fee drag on returns.

The net value of the assets an ETF holds. AUM indicates fund scale, but it does not by itself determine liquidity or trading costs; bid-ask spreads, trading volume, market makers and the liquidity of underlying holdings also matter. AUM changes with market prices and fund inflows or outflows.

One. The Global X Hydrogen ETF (HYDR) is the only US-listed ETF whose stated investment objective is hydrogen. A fund qualifies for this list if its prospectus objective is hydrogen exposure — production, fuel cells, electrolysers, hydrogen infrastructure or hydrogen integration. Broad clean-energy and energy-transition ETFs that happen to hold a few hydrogen names, such as fuel cell makers inside a wider renewables basket, are excluded, because their objective is the wider basket. Two dedicated funds have closed: Direxion's HJEN in July 2024 and Defiance's HDRO in April 2025.

HYDR tracks the Solactive Global Hydrogen Index, which includes companies involved in hydrogen production, hydrogen fuel cell manufacturing, and hydrogen energy system integration across global markets.

HYDR invests in companies across the hydrogen value chain, including hydrogen producers, fuel cell manufacturers like Bloom Energy and Plug Power, electrolyzer makers like ITM Power, and companies integrating hydrogen into broader energy systems.

Two dedicated hydrogen ETFs have been liquidated. The Direxion Hydrogen ETF (HJEN) went first: Direxion filed a supplement on 21 June 2024, shares ceased trading on NYSE Arca at the close on 19 July 2024, and the fund liquidated on or about 30 July 2024. Direxion's adviser told the board the fund could not be run economically over the long term because of its inability to attract sufficient investment assets. The Defiance Next Gen H2 ETF (HDRO) followed nine months later: a Rule 497(e) supplement filed on 14 April 2025 said the board, on a recommendation from Defiance ETFs, had determined to close and liquidate the fund immediately after the close of business on 29 April 2025. That filing gives no reason for the decision.

HYDR's own 2026 prospectus is specific about them. The fund is non-diversified, so a move in one holding can move the NAV more than it would in a diversified fund. Many hydrogen companies are early in their operating lives, carry smaller market capitalisations than companies in established sectors, and their securities are considerably more volatile than those of more established industries. Returns depend heavily on tax incentives, subsidies and government policy, and the prospectus draws an explicit distinction between policy implemented in legislation and commitments that are aspirational and harder to enforce. A fall in the price of conventional energy such as natural gas can hurt hydrogen companies directly by making their output less competitive. Most holdings are listed outside the US, adding currency and geographic risk, and the fund's use of cash creations and redemptions can widen spreads and reduce tax efficiency relative to a conventional ETF.