Localized electrochemically grown porous platinum layers on 2D and 3D microstructured materials enable a wide range of applications from electrocatalysis to optoelectronics. These layers exhibit a thickness gradient and surface corner overloading due to electric charge accumulation at the sharp corners. On one hand, these effects can be applied to create ultra-large surface area catalysts or electrocatalysts. On the other hand, they can be mitigated by guiding the electric field at the nanoscale. Here, we show that porous platinum grown on rough conductive silicon synergistically catalyses the electroreduction of CO2 in a humid gaseous atmosphere, overcoming the disadvantage of CO2´s low water solubility. In addition, using template-directed growth of porous platinum, we tuned the optical response of an infrared (IR) metamaterial fabricated by micropatterning on Si/NiCr/Ti substrates and constructed a broad absorber on potential IR-functional microcomponents.