Catalytic reduction of O-2 at metal catalysts either follows a 2-electron transfer pathway to the formation of H2O2 or a 4-electron transfer pathway to the formation of H2O. The branching ratio of this reaction has a significant impact on the applicability of catalyst materials. The previously introduced oxygen competition mode of SECM, which allows high-resolution imaging of local O-2 consumption, has been extended to a potential-pulse sequence enabling the sequential detection of O-2 reduction followed by the detection of local H2O2 formation. Thus, not only the local catalytic activity of a catalyst can be visualised but, additionally, the degree of the branching can be estimated. The selectivity of a catalyst candidate can thereby be visualised sequentially to the elucidation of its activity. First results on the properties of electrodeposited Pt and An test structures are shown demonstrating the feasibility to clearly distinguish catalyst activity and selectivity under variation of the polarisation potential. (c) 2007 Elsevier Ltd. All rights reserved.