As the world tackles climate change, reducing greenhouse gas (GHG) emissions is essential. The maritime industry, responsible for about 3% of global CO2 emissions, is under pressure to adopt greener practices. Onboard Carbon Capture and Storage (OCCS) technology offers a promising solution by capturing CO2 from ship exhausts and storing it for later use or disposal. This article explores OCCS in detail, covering its technology, current developments, challenges, and future potential, aiming to guide stakeholders in its role in maritime decarbonization.

Technological Foundations of OCCS OCCS systems combine carbon capture, storage, and offloading processes designed for ships. Key methods include post-combustion capture, pre-combustion capture, and oxy-fuel combustion. Post-combustion capture, using chemical absorption with amines, is the most developed approach, separating CO2 from exhaust gases, compressing it into a liquid, and storing it in onboard tanks. Pre-combustion capture converts fuel into a gas mixture, removing CO2 before combustion, often for hydrogen use. Oxy-fuel combustion uses oxygen, producing a CO2-rich exhaust for easier capture. These methods require energy, affecting efficiency, and need compact designs due to limited space. Storage can be liquid, gaseous, or solid, with liquid being the most practical due to existing infrastructure.

Current Developments and Pilot Projects Recent progress shows OCCS's potential. In 2025, the Clipper Eris, an LPG tanker by Solvang ASA, was retrofitted with Wärtsilä's OCCS technology, achieving a 70% CO2 capture rate. Supported by MAN Energy Solutions and SINTEF, it tests storage in deck tanks for offloading. Hanwha Ocean and GasLog also retrofitted LNG carriers with efficient OCCS systems, targeting completion by 2024. The Oil and Gas Climate Initiative (OGCI) and Global Centre for Maritime Decarbonisation (GCMD) found OCCS reduced emissions by 20% on the Stena Impero, with a 10% fuel penalty. These projects highlight the need for port infrastructure, which remains limited for CO2 offloading.

Challenges Facing OCCS Implementation OCCS faces several obstacles. Limited onboard space restricts the size of capture and storage units, demanding innovative designs. The energy needed for capture and liquefaction lowers fuel efficiency, raising costs. Initial investment is high, with the Stena Impero retrofit costing $13.6 million, though costs may drop with scale. Regulatory uncertainty adds complexity, as the International Maritime Organization (IMO) lacks standardized safety and emissions rules. Few ports can handle liquefied CO2 (LCO2), creating logistical issues. Economic viability depends on carbon pricing and incentives, which are currently inadequate.

Future Prospects and Recommendations OCCS's future relies on technological improvements and collaboration. Advances like membrane separation or cryogenic methods could lower energy use. Port infrastructure for CO2 offloading and storage needs significant investment from governments and industry. Clear IMO regulations, including carbon pricing, will boost adoption. As a transitional technology, OCCS can complement zero-carbon fuels like hydrogen. A phased approach, starting with OCCS-ready ships, allows adaptation while awaiting clean energy solutions. Stakeholders should focus on pilot data, infrastructure, and policy support to meet the IMO's 2050 net-zero goal.

OCCS is a key step toward decarbonizing maritime transport, offering a near-term emissions reduction tool. Pilot projects show promise, but challenges in space, cost, and infrastructure must be overcome. With innovation and policy support, OCCS can bridge the gap to a carbon-neutral maritime future.