Heat and mass transfer of Ag–H<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si93.svg" display="inline" id="d1e1412"><mml:msub><mml:mrow/><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:math>O nano-thin film flowing over a porous medium: A modified Buongiorno’s model