I dont suggest brush coating technique for coating carbon films on metal. Doctor blade technique or even squege method (using glass rod) will give far better results. However, the slurry should be viscous enough. PVDF(Teflon)/Carbon is generally used for making electrodes for lithium ion batteries and is being recently adopted for DSSCs also. So, I think it is a good combination. In my work, I have used other solvents such as ethanol or ethanol:Nafion but CNTs/graphene had to be functionalized in order to be dispersed.

And what is the better combination to make carbon counter electrodes in metal substrates?

Screen printing,air-brush,or e-spray.It depends on the properties of your carbon material. if the particle diameter of the as prepared carbon is lager, then the first method isn't recommended,otherwise I think it is a good way to prepare CEs.You should first mixed your simple with PEO or PVDF to from a viscous slurry, and then do it in the way you prepare photoanode via screen printing.Between the latter two, air-brush is more convenient, you just need an air compressor and a  spray gun, but it will waste a lot of your sample.If you can make the sample with large amount,I suggest you employ airbrush.The last method, you should first make a homogeneous solution consisting of your sample and isopropanol via ultrasonic  dispersion.Then using a injection syringe which is connected to the positive side of  a power supply,along with your FTO fixed on a metal panel which is connected to the negative side of the power supply.then run the  injection syringe with a constant pushing rate and simultaneously turn on the power supply.I will choose this way at last due to its difficulty to control the uniformity of the CEs.