A final notable difference to performing CO2 electroreduction in an H-cell versus a gasdiffusion layer configuration is subtler. As has been recently demonstrated, under high current density operation the CO2 reduction reaction is confined to a relatively small portion of a porous catalyst layer and takes place on the backside of the material (Fig. ). This is in contrast to an H-cell where CO2 diffuses to the catalyst layer from the front-side bulk electrolyte (Fig. ). Much like the effects of varying morphology and porosity in H-cell catalyst studies allowed for performance to be improved and varied, the reversed flow direction of CO2 transport allows for unique gas-diffusion and catalyst layer engineering to take place. One recent example is placing an inactive material on top of the catalyst layer (Fig. ) to provide an additionally conductive layer. While this layer is used as a current collector, it may also help to prevent both catalyst restructuring that can change catalytic behaviour as well as the deposition of contaminants on the active catalyst surface.