An integrated vehicle on-board system configured to generate hydrogen and to introduce the generated hydrogen into an exhaust gas stream of an internal combustion engine, the system including a water-splitting article configured to split water into hydrogen and oxygen and a hydrogen injection article configured to introduce the hydrogen into the exhaust gas stream, is effective for the abatement of carbon monoxide and/or hydrocarbons and/or nitrogen oxides. The introduction of hydrogen may be intermittent and/or during a cold-start period.