Seawater splitting represents an inexpensive and attractive route for producing hydrogen, which does not require a desalination process. Highly active and durable electrocatalysts are required to sustain seawater splitting. Herein we report the phosphidation-based synthesis of a cobalt–iron–phosphate ((Co,Fe)PO₄) electrocatalyst for hydrogen evolution reaction (HER) toward alkaline seawater splitting. (Co,Fe)PO₄ demonstrates high HER activity and durability in alkaline natural seawater (1 M KOH + seawater), delivering a current density of 10 mA/cm² at an overpotential of 137 mV. Furthermore, the measured potential of the electrocatalyst ((Co,Fe)PO₄) at a constant current density of −100 mA/cm² remains very stable without noticeable degradation for 72 h during the continuous operation in alkaline natural seawater, demonstrating its suitability for seawater applications. Furthermore, an alkaline seawater electrolyzer employing the non-precious-metal catalysts demonstrates better performance (1.625 V at 10 mA/cm²) than one employing precious metal ones (1.653 V at 10 mA/cm²). The non-precious-metal-based alkaline seawater electrolyzer exhibits a high solar-to-hydrogen (STH) efficiency (12.8%) in a commercial silicon solar cell.

Paris agreement’s goal was to the increase in the global average temperature to well below 2℃ above pre-industrial levels and limit global temperature increase to 1.5℃ above pre-industrial levels. The International Maritime Organization (IMO) has reinforced regulations regarding sulfur content, aiming to limit the sulfur content of ship fuel oil from 3.5% to 0.5% from 2020. LNG fuel contains a small amount of sulfur, enabling compliance with IMO’s sulfur content regulations and effectively reducing carbon emissions. However, the main component of LNG is liquefied methane, which has limitations due to methane emissions generated during LNG production, transportation, and distribution. Hydrogen energy is in the spotlight as an alternative fuel to significantly reduce greenhouse gases such as carbon monoxide, carbon dioxide, and methane. In the case of liquid hydrogen, rather than gaseous hydrogen, the volume is reduced to 1/800, increasing the storage and transport efficiency of hydrogen by about seven times. Additionally, there is an advantage that a separate dehydrogenation process is not required. The most promising material for liquefied hydrogen tanks is austenitic stainless steel (ASS), although there are various materials that can be considered. It is expected that the use of ASS will be actively pursued in the future, especially for applying storage tanks to maritime transportation, where welding is essential. Evaluation methods of the physical properties of the weld in a cryogenic atmosphere for the stability of the liquefied hydrogen storage tank were also discussed.