Electrochemically Active Surface Area (ECSA) determination: The ECSA of each catalyst was determined by measuring the electrochemical double-layer capacitance (Cdl) of each catalyst from the scan-rate dependence of the CV plot. Four different CV measurements were performed at a potential window between 0.72 to 0.82 V (vs the reversible hydrogen electrode) on each catalyst at scan rates of 20,30, 40 and 50 mV/s respectively. The Cdl was estimated at the average potential within this range by calculating the slope of the linear fit at that point. A specific capacitance (Cs) of 40 μF/cm 2 was used to calculate the ECSA of the catalyst using the following equation: