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Catalyst poisoning from the impurities in the industrial grade methanol is a major challenge for the large-scale application of direct methanol fuel cells in low cost. In this work, we systematically investigate the impurities influencing on cell performance, and confirm that the adsorption of carbonyl containing intermediate species derived from the partial electro-oxidation of the impurities is a crucial factor leading to performance degradation. Hence, an on-line alleviation strategy by intermittently applying pulse potential (reduction potential on the anode or oxidation potential on the cathode) is proposed. The applied potential will bring a reductive condition on the anode, which releases the active sites via the reduction of carbonyl containing species adsorbed on platinum-ruthenium electro-catalysts. Based on this strategy, the adsorption of carbonyl containing intermediate species are effectively suppressed, and the decay rate declines by nearly two orders of magnitude than that of a single cell under traditional operation, which paves a way for the practical application of direct methanol fuel cells with industrial grade methanol feed.