1. Introduction

Various technologies are being developed both domestically and internationally to reduce air pollutants such as sulfur oxides, nitrogen oxides, and greenhouse gases emitted from ships. In particular, the international maritime sector, centered on the International Maritime Organization (IMO), is gradually strengthening ship emission regulations to achieve the “Net Zero” carbon emissions goal by 2050 compared to 2008 levels. In this trend of tightening environmental regulations, the shipping industry is now required to actively develop eco-friendly ship technologies and apply them in full-scale ship operations (IMO, 2025).

One of the most proactive approaches to reducing emissions from ships includes the use of alternative fuels and changes in propulsion systems. Among these, electric propulsion systems are gaining attention as an alternative that can enhance the environmental performance of ships. In particular, hybrid electric propulsion systems using fuel cells and batteries as power sources are emerging as promising propulsion methods for next-generation eco-friendly vessels, thanks to their zero-emission characteristics and high energy efficiency (Kim and Jeon, 2022).

Marine fuel cells used as power sources in electric propulsion systems offer significantly reduced vibration and noise compared to conventional diesel engines used in mechanical propulsion systems. They can also achieve high efficiency through waste heat recovery and enable operation with no pollutant emissions. Meanwhile, batteries can quickly respond to rapid load fluctuations on ships and sudden peak power demands, thereby enhancing the stability and operational flexibility of the propulsion system. A hybrid electric propulsion system that integrates such eco-friendly power sources is being evaluated as a reliable alternative suitable for various maritime environments.

Particularly, ammonia used to extract hydrogen for fuel cells has a higher volumetric energy density compared to hydrogen, is highly compatible with existing storage and transportation infrastructure, and emits no carbon dioxide (CO₂), one of the major greenhouse gases, after reaction (Alias et al., 2020). For these reasons, ammonia is being actively studied as a viable alternative fuel for marine applications. However, since ammonia cannot be directly supplied to fuel cells as a fuel, it can only be used as a hydrogen storage medium on fuel cell ships. Hydrogen must be extracted through chemical reactions using a separate reformer. Critical technical issues in this reforming process include ammonia slip, ensuring the safety of the reactor, and supplying power for high-temperature operation.

Currently, various countries including Korea are conducting demonstration studies for developing fuel cell-battery hybrid electric propulsion systems that utilize ammonia reformers, which are applicable to eco-friendly marine propulsion systems. Most of these studies are government-led and involve shipyards, shipping companies, classification societies, fuel cell-related companies, and research institutes (KR, 2025a). However, standardized test items, procedures, and quantitative criteria for performance verification and safety evaluation required prior to the installation of developed equipment on ships are still lacking. In particular, there is currently no established standardized testing framework for reformers for reformers, which are key components of the fuel supply system critical to the operation of fuel cells, for use in marine applications.

Therefore, this study aims to provide foundational data for establishing future test standards by systematically identifying technical characteristics of ammonia reformers applied in fuel cell-battery hybrid electric propulsion systems, deriving test items and procedures based on ship operation environments, and evaluating the validity of the major test categories for performance verification of reformers intended for marine installation.

2. Analysis of Domestic and International Technological Trends and Standards for Test Item Development

2.1 Absence of Certification Standards for Marine Ammonia Reformers

Currently, there are virtually no established domestic or international standards for the testing and certification of marine ammonia reformers. The application of ammonia as a marine fuel remains in its early stages of technological implementation, and no official test items, procedures, or certification criteria have yet been defined to validate the developed technologies. For instance, the “IGF Code” a set of safety regulations for low-flash point fuels established by the International Maritime Organization (IMO) mainly focuses on LNG fuels and includes only limited technical requirements, while separate standards for other fuels such as ammonia have yet to be developed (KR, 2025b).

Similarly, in South Korea, the “Act on the Promotion of Development and Distribution of Environment-Friendly Ships,” which was announced in January 2020, specifies that electricity generated using hydrogen and other sources may be used as a propulsion energy source (Jeon et al., 2022). However, concrete test standards for inspecting ships equipped with marine fuel cells based on ammonia reformers have not been established, creating significant obstacles for actual onboard application of developed equipment. This lack of certification protocols for emerging technologies hinders the practical adoption of advanced eco-friendly propulsion systems in maritime applications.

As a result, some countries and classification societies have begun applying preliminary approval (AIP) procedures or provisional guidelines on a project-by-project basis. For example, Norway granted AIP for the world’s first retrofit project involving a 2 MW ammonia fuel cell propulsion ship, scheduled for 2024. This case is being evaluated as an attempt to verify the technical feasibility and safety of new technologies through individual applications (AMMONIA ENERGY, 2024).

2.2 Trends in Related International Standards

Fuel supply systems utilizing marine ammonia reformers currently fall into a technical blind spot within the framework of existing international standards. The IMO has developed the IGF Code to provide detailed requirements for applying LNG fuel to ships, but specific regulations for other fuels, including ammonia, are planned to be addressed in the future through supplemental standards (KR, 2025). In fact, while discussions have taken place within the IMO's Sub-Committee on Carriage of Cargoes and Containers (CCC) to develop guidance for methanol and LPG fuels, guidelines for ammonia fuel have not yet been finalized.

In addition, although international standardization bodies such as the International Electrotechnical Commission (IEC) and the International Organization for Standardization (ISO) have established standards related to fuel cells, these mainly pertain to stacks, modules, and systems. There is no mention of reformers used to supply hydrogen fuel. For example, the “IEC 62282 series” addresses safety and performance requirements for fuel cell systems, but it does not include provisions for testing and certifying systems that use ammonia reformers to supply hydrogen to fuel cells (IEC, 2020).

Meanwhile, the equipment standards for marine fuel cells have been partially addressed by the IMO through the issuance of “Interim Guidelines for the Safety of Ships Using Fuel Cell Power Installations” (IMO MSC.1/Circ), which was officially published following its approval at the 105th MSC meeting (KR, 2025b). While this guideline covers design and construction criteria for ships using fuel cell power systems, it does not yet include specific standards addressing issues such as toxicity, corrosiveness, leakage characteristics, or thermal reaction behaviors in the case of ammonia-fueled systems.

2.3 Analysis of Global Trends and Application Cases of Ammonia Fuel Cell Technologies by Country

Fuel The development of fuel cell–battery hybrid electric propulsion systems using ammonia fuel is being pursued in various forms both domestically and internationally. These technology trends and application cases can serve as valuable references for establishing test items and procedures applicable to ammonia reformers.

(1) Norway

Norway is one of the most active countries in the adoption of eco-friendly ships. The vessel Viking Energy, developed through the “ShipFC Project,” has applied a 2 MW-class solid oxide fuel cell (SOFC) system powered by ammonia fuel and obtained Approval in Principle (AIP) in 2024. Additionally, the company Amogy successfully conducted sea trials with the tugboat NH₃ Kraken, which is equipped with a fuel cell system based on an ammonia cracker (AMMONIA ENERGY, 2024).

(2) Germany and Europe

Germany’s Fraunhofer IMM has developed a small-scale ammonia reformer that supplies hydrogen fuel to marine PEMFCs and is conducting demonstration tests. Through various European projects, evaluation criteria are being established for hydrogen quality, safety, and production rates in response to load variations when hydrogen is produced via reformers (Fraunhofer, 2021).

(3) Japan

Japan’s NYK Line and IHI Power Systems collaborated to construct and demonstrate the world’s first ammonia-fueled tugboat, Sakigake, in 2024. The vessel operates on a mixed-fuel system combining ammonia and diesel. It was reported that when the co-firing ratio reached 95%, greenhouse gas emissions were reduced by a similar percentage (NYK Group, 2024).

(4) Republic of Korea

The Ministry of Oceans and Fisheries has established the “Interim Guidelines for Hydrogen Fuel Cell Installations on Ships” to support the design and construction of vessels applying new technologies. The Korea Institute of Energy Research (KIER) has developed reformer technology based on PSA (Pressure Swing Adsorption), capable of producing ultra-high purity hydrogen (99.99%) and reducing residual ammonia concentration in hydrogen to below 0.1 ppm (Ibrahim et al., 2025).

Based on this analysis of domestic and international standards and technology development trends, it can be observed that demonstration research related to applying ammonia reformers to marine systems is being actively conducted, particularly abroad. However, there remains a significant lack of test and certification procedures to support the practical application of these technologies. For reformers using ammonia fuel, key technical considerations include the discontinuity of hydrogen production, stability at high reaction temperatures, control of ammonia slip, and responses to corrosion and leakage caused by ammonia. Therefore, it is essential to develop evaluation items for reliable performance testing.

Accordingly, this study aims to propose performance test items and procedures for marine ammonia reformers that reflect the current level of technological maturity, thereby providing a foundation for establishing initial technical standards to ensure the reliability of future verification of ammonia reformers used in ships.

3. Derivation and Validation of Test Items for Marine Reformers

3.1 Configuration and Types of Marine Reformers

The ammonia reformer applied to fuel cell-battery hybrid electric propulsion systems for ships refers to a system that produces high-purity hydrogen from ammonia, which is required for fuel cell operation. Since the system is intended to be installed on ships with limited space, it must consider constraints such as installation volume, weight, the hydrogen purity requirements of the fuel cell, and ship operating conditions. In this study, two types of reformer systems are classified based on whether a hydrogen purification process is applied (Yáñez et al., 2019).

(1) Reformer System with PSA (Pressure Swing Adsorption)

As shown in Fig. 1, This system decomposes ammonia supplied from the ammonia fuel tank into hydrogen and nitrogen through a reformer operating at a high temperature of 600-650 °C. It then passes through an ammonia remover and a PSA process to produce high-purity hydrogen with a concentration exceeding 85%. The unrefined gas is recovered and reused as a heat source via a burner. As the system must meet hydrogen quality standards applicable to fuel cells, it is suitable for highly sensitive fuel cells such as PEMFC (Proton Exchange Membrane Fuel Cell) that require ultra-high purity hydrogen.

(2) Reformer System without PSA (Pressure Swing Adsorption)

As depicted in Fig. 2, This system omits the PSA process and consists only of a reformer and an ammonia remover to produce hydrogen. The resulting mixed gas is directly supplied to the fuel cell without further purification. Compared to reformers using PSA, this system produces hydrogen of relatively lower purity (H₂ > 75%). Therefore, it is applied to fuel cells that can operate with such hydrogen quality. Additionally, it is suitable for small- to medium-sized vessels with limited space or for systems where load fluctuations during ship operation are minimal and the hydrogen purity requirements are relatively low.

3.2 Derivation of Test Items for Marine Reformers

To install a reformer an essential component for using ammonia as fuel in marine fuel cells it is necessary to establish objective and quantitative criteria for evaluating the performance and safety of the device. In particular, since ships operate in maritime environments that are more susceptible to hull motion, inclinations, and vibrations caused by waves compared to land-based systems, it is essential to quantitatively assess whether the operating characteristics of the reformer remain stable under such conditions.

This study aims to derive test items that can quantitatively evaluate the applicability of ammonia fuel reformers for use in fuel cell–battery hybrid electric propulsion systems on ships. These derived items can serve as foundational data for establishing future domestic and international standards for ammonia-based propulsion systems.

The objectives of deriving test items for marine ammonia reformers are as follows: First, to verify the applicability of reformers and fuel cell systems when installed and operated on actual ships by acquiring quantitative data on operational characteristics, output stability, and hydrogen supply capability under maritime conditions. Second, to assess the reformer’s performance under marine operational conditions such as tilt, vibration, and load variation, by identifying potential risk factors in advance taking into account ammonia fuel’s inherent properties such as toxicity, corrosiveness, potential for ammonia slip, and thermal reaction behavior. These test items must faithfully reflect real-ship operating conditions on ships and allow for repeatable and reproducible testing. Therefore, the criteria were derived to meet the following standards, as shown in Table 1 below.

Based on the above system configurations, the four key test items derived for the reformer are as follows.

(1) Hydrogen Production Rate

The maximum hydrogen production rate of the marine ammonia reformer, as well as its supply capability under partial load conditions, is quantitatively evaluated. Depending on the total capacity of the reformer, the hydrogen production rate (Nm³/h) is measured at 25%, 50%, 75%, and 100% load levels in an environment without vibration or inclination. This item serves as a key indicator for determining whether the reformer can continuously and stably supply the hydrogen required by the fuel cell system. In particular, the test is linked with vibration and inclination conditions essentially encountered during ship operation to simulate a marine environment and verify that the hydrogen production rate (Nm³/h) does not degrade under such conditions. The selected load levels of 25%, 50%, 75%, and 100% are based on standard load conditions typically applied during commissioning of fuel processing systems. As shown in Table 2 below, the test procedures and items are described.

(2) Hydrogen Purity

The purity of hydrogen (H₂) in the reformed gas produced by the marine reformer is measured, along with the concentrations of impurities such as ammonia (NH₃) and nitrogen (N₂). In particular, PEMFC require high-purity hydrogen supply. According to ISO 14687, systems equipped with a PSA process are required to achieve hydrogen purity of 85% or higher based on the reformer’s hydrogen production rate, while systems without PSA should meet a minimum hydrogen purity of 70%. As shown in Table 3 below, the test procedures and items are described.

(3) Residual Ammonia Slip

This test quantitatively measures the concentration of unreacted residual ammonia at the outlet of the reformer and the inlet of the fuel cell. It evaluates the ammonia removal performance of the reformer to determine whether the hydrogen quality meets the requirements for use as fuel in fuel cells. During the test, ammonia concentrations are measured at both the reformer outlet and the fuel cell inlet to verify compliance with the ISO 14687 standard, which specifies a maximum residual ammonia concentration of 0.1 ppm. The test procedures and items are presented in Table 4 below.

(4) Inclination/Heel Stability Test

The inclination stability test is conducted to verify whether the reformer installed on a ship can continuously and stably produce hydrogen under simulated marine operating conditions, and to comprehensively assess its thermal and mechanical stability in a maritime environment. To evaluate the reformer’s adaptability and safety under marine operating conditions, the reformer is tested while operating normally with a longitudinal inclination of 10° and a transverse inclination of 22.5°, performing inclination tests along three axes for at least 15 minutes. The test evaluates the dynamic response of the ammonia reformer under load variations, while recording and verifying the hydrogen production rate, hydrogen purity, and ammonia slip concentration during the inclination test. The test procedures and parameters are detailed in Table 5 below.

3.3 Derivation of Test Items for Marine Reformers

To practically apply marine fuel cell systems, it is essential to ensure high reliability and safety under the harsh and rapidly changing operational conditions unique to shipboard environments, including space limitations and marine dynamics. In particular, hybrid propulsion systems based on fuel cells must respond quickly to variations in hydrogen fuel purity, load fluctuations, and the dynamic interaction and control characteristics between the reformer and the fuel cell system. Therefore, a quantitative and validated testing framework is required to ensure stability and continuous operation during actual shipboard use.

The four major test items derived in this study are essential evaluation indicators to verify the applicability of ammonia reformers for marine applications. The technical validity of each item is as follows:

(1) Hydrogen Production Rate

The ammonia reformer plays a critical role in supplying the hydrogen required by the fuel cell in real-time, depending on load fluctuations. Its hydrogen production capacity is a key factor that can directly impact the output performance of the entire ship propulsion system. In hybrid propulsion systems, hydrogen consumption by the fuel cell system dynamically varies with real-time changes in propulsion load. If the onboard reformer fails to respond adequately to these changes, it may result in reduced fuel cell output, propulsion loss, delayed transient responses, or in the worst-case scenario, complete shutdown of the propulsion system, leading to serious accidents. Therefore, verifying whether the reformer can stably maintain the target hydrogen production rate (Nm³/h) not only under rated conditions but also under transient and fluctuating load conditions is a critical test to ensure system continuity and stability.

(2) Hydrogen Purity

High-performance fuel cells such as PEMFC are highly sensitive to the purity of the supplied hydrogen. Impurities in the hydrogen supply (e.g., ammonia, nitrogen, moisture, hydrocarbons) can lead to catalyst poisoning in the fuel cell stack, resulting in unstable output voltage, reduced system output, and overall performance degradation. According to ISO 14687, hydrogen supplied for fuel cells must contain no more than 0.1 ppm of ammonia and must maintain hydrogen purity of at least 99.97%. Therefore, it is essential to establish purity standards for hydrogen produced by onboard reformers, measure them quantitatively, and confirm compliance as a critical test item.

(3) Residual Ammonia Slip

Due to the thermodynamic equilibrium limitations of the ammonia reforming reaction, unreacted ammonia may remain in the reformed gas, resulting in ammonia slip. This residual ammonia can cause catalyst deactivation in the fuel cell stack, shorten the fuel cell’s lifespan, and result in atmospheric pollution or toxic gas leakage inside the vessel. Such issues can be especially critical in enclosed spaces like ship engine rooms. Therefore, it is a highly valid test to precisely measure the ammonia concentration in ppm levels at the reformer outlet and fuel cell inlet and to verify whether it is maintained below the threshold using purification processes such as ammonia absorbers and PSA.

(4) Inclination/Heel Stability Test

Ships operate under dynamic conditions such as heel, pitch and roll, and vibration for most of their operational time except when docked. These operating conditions can directly affect fluid flow, reaction stability, and heat transfer inside the reformer. Moreover, ammonia requires high precision in reaction control, and problems such as asymmetric fluid supply, thermal reaction imbalance, and increased ammonia slip may arise due to ship inclinations. Therefore, simulating realistic ship inclination conditions such as longitudinal and transverse tilts—and quantitatively evaluating variations in hydrogen production rate, reactor temperature, and ammonia slip concentration is a technically justified and essential test to ensure the reformer's operational reliability at sea.

4. Conclusion

In this study, we systematically derived and standardized the test items and procedures necessary for evaluating the maritime applicability of fuel cell-battery hybrid electric propulsion systems equipped with ammonia reformers. Despite ammonia’s high potential as a carbon-free fuel to reduce ship emissions in the future, standardized test performance evaluation criteria and procedures for reformers suitable for onboard use are still lacking both domestically and internationally.

To address this, the study derived key test items hydrogen production rate, hydrogen purity, residual ammonia slip, and inclination stability based on the IMO IGF Code, various national classification society regulations, and existing research. These test items were developed with clear evaluation purposes and indicators, reflecting the operational characteristics of integrated reformer fuel cell systems and providing a quantitative verification framework for shipboard applicability.

These proposed and repeatable test items are expected to serve as foundational data for future certification, classification approvals, and the development of domestic and international standards. Furthermore, they have significance as precedent research for application in follow up demonstration studies, onboard test trials, and standardization processes.