An internal combustion engine system includes an internal combustion engine, an exhaust aftertreatment system with a catalytic converter configured to receive exhaust gas from the internal combustion engine, and a light-off catalyst system including an electrolyzer configured to perform an electrolysis of water to produce a mixture of hydrogen and oxygen gases. A conduit is in fluid communication between the electrolyzer and an intake of the internal combustion engine. A controller is configured to supply the mixture of hydrogen and oxygen gases to the engine intake during a cold start to facilitate rapidly warming the catalytic converter to a light-off temperature.

In a method for exhaust gas aftertreatment, in which an exhaust gas to be aftertreated, which is produced during combustion of a fuel, is treated with a reducing agent. A constituent of the fuel is hereby also used as a constituent of the reducing agent, with the constituent of the fuel which is also used as a constituent of the reducing agent being hydrogen. The hydrogen is produced from water, and the reducing agent is a mixture of hydrogen and ammonia.

A process for capturing carbon dioxide (CO.sub.2) emissions and converting the CO.sub.2 into an alcohol fuel is disclosed herein. The process includes capturing CO.sub.2 emissions from an exhaust mechanism of a machine at a CO.sub.2 capture device. The process also includes converting the CO.sub.2 emissions into an alcohol fuel using an electrolyzer.