The true surface area or electrochemically active surface area can be measured only for some metal electrodes such as Pt, Au, Pd , Ni etc., but not for say, carbon based electrodes or metal oxide electrodes.  Electrochemically active surface area( ECSA) is usually considered for specifying the current density when the electrode material is a  mesoporous surface, for example, an electro catalyst.  The normalization procedure is resorted to,  by taking into account any  variation in the true surface area during different measurements with different samples.  This will help in comparison studies with other similar  electrodes. 

In your case, if the electrode being used in RDE is a smooth one  and can be reproduced easily during every experiment by polishing and simple surface treatment  it is  O.K.  to  mention the current density wrt to the geometric area. In fact some of the basic studies on the electron transfer kinetics is done using such electrodes.

Thank you Dr.Lakshminarayanan. so how to compare activities between different type catalysts？should i using special activity or mass special activity?

when i use origin to draw a figure of polarization curves, is it necessary to make Y-axis normalized? Such as  acid condition normalized to 6 mAcm-2, while alkaline solution to 4 mAcm-2.

Activities of the different electrodes have to be compared with the respective mass of the catalysts and the current density should be with respect to mass of the catalyst alone in the electrode.

I do not understand the second question. If your question is on the process of  normalization, it has to be carried out with respect to ECSA ( as determined by a standard procedure of charge measurement using CV) whether  it is in acid or alkaline medium. 

Current density is defined as the current produced during ORR divided by the area of the working electrode which can be the geometric area or more specifically the electroactive area ECSA.  In any case it has to be indicated.  ECSA can be estimated by using several methods : if platinum is included in the electrocatalyst ECSA can be calculated from the CV in the hydrogen adsorption-desorption zone. If the CV does not show those characteristic peaks then CO adsorption technique can be used for obtaining ECSA. Additionally, depending on the electrocatalyst it can be employed the Cu UPD (copper underpotetentially deposited). 

To compare electrocatalyst activity the most common parameters are Specific Activity and Mass Activity but don´t forget about overpotential.

Thank you Dr. Miguel ANGEL García-Contreras. The methods of determination electrocatalyst ECSA which you have mentioned are most about electrocatalyst ffor noble metal catalyst, i want to obtain electrocatalyst ECA of metal oxide, which mathod can obtain? because i want to calculate the specific current density. i don't know the roughness factor of of the catalyst, can i use geometric area to substitute electrochemical area or real area of electrode?

Dr.Lakshminarayanan can you help which figure is right? the catatyst is hybrid metal oxide, i test  line sweep voltammetry in alkaline medium at 1600rpm. is it necessory  to be carried out with respect to normalizing  the maximum of Y-axis is normalized

to 4 mA cm-2 in  alkaline medium. which figure is right? thank you very much.

Normalization cannot be carried out arbitrarily with respect to any current density. If you are representing the value of a single electrode and when no comparison is involved, then you don't need to perform normalization and just present the raw data with respect to the geometric area.   Geometric area is O.K. as long as the surface is smooth and can be reproduced by standard polishing protocol.

Check these Articles :

1) J. Electrochem. Soc. 161 (3) H121-H128 (2014) H121

Determination of the Electrochemically Active Surface Area

of Metal-Oxide Supported Platinum Catalyst

T. Binninger, E. Fabbri, R. Kotz, T. J. Schmidt

2) J. Electrochem. Soc. 162 (12) F1292-F1298 (2015)

Calculating the Electrochemically Active Surface Area of Iridium

Oxide in Operating Proton Exchange Membrane Electrolyzers

Sh Zhao, H Yu, R Maric, N Danilovic, Ch B. Capuano, K E. Ayers, W E. Mustaina

Dr. Lakshminarayanan is completely right : You can refer the current density to the geometric area only if you have a working electrode with smooth surface, e.g. a glassy carbon disk previously polished to a mirror finish with a Al2O3 particle suspensión.