An electrocatalyst including a substrate and Co.sub.xNi.sub.yFe.sub.2O.sub.4 nanoparticles, where x+y=1. The Co.sub.xNi.sub.yFe.sub.2O.sub.4 nanoparticles are doped with 0.01 weight percentage (wt. %) to 1.0 wt. % selenium (Se), based on the total weight of the Co.sub.xNi.sub.yFe.sub.2O.sub.4 nanoparticles. Further, the Co.sub.xNi.sub.yFe.sub.2O.sub.4 nanoparticles have a polygonal shape, and the Co.sub.xNi.sub.yFe.sub.2O.sub.4 nanoparticles are dispersed on the substrate to form the electrocatalyst.

A counter-rotating roller system for coating electrode materials includes a roll-to-roll apparatus including a dispensing roller that selectively dispenses a conductive substrate from a substrate roll along a first direction towards a receiving roller. A counter-rotating roller module including a counter-rotating roller is stationarily positioned at a predetermined height over the conductive substrate. The direction of the tangential velocity of the counter-rotating roller at an interface between the counter-rotating roller and the conductive substrate is 180 degrees opposite the first direction of travel of the conductive substrate. The system further includes a continuous powder application module positioned on a feed side of the counter-rotating roller to continuously deposit a volume of a dry powder mixture on the conductive substrate prior to contact with the counter-rotating roller. A contact roller scraper contacting the counter-rotating roller removes powder particles from an outer surface of the counter-rotating roller.

A cathode structure of a fuel cell is disclosed. The cathode structure comprises a cathode diffusion layer, wherein an air permeability adjusting structure is arranged around the cathode diffusion layer, and the cathode air permeability of the air permeability adjusting structure gradually varies in the flow direction of fluid. According to the cathode structure of a fuel cell, by means of arranging the air permeability adjusting structure, with variable cathode air permeability around the cathode diffusion layer, the difference caused by different temperatures and humidity is subtly compensated for, thus improving the problem of water accumulation or dehydration in a cathode structure of a fuel cell, and effectively improving the water management of the fuel cell.