Twisted PdCu nanochains are synthesized successfully via a staged thermal treatment route, offering rich twin boundaries as catalytic "active sites" and modified electronic effects. Toward formic acid oxidation, the twisted PdCu nanochains hold the highest catalytic peak current density (1108.2 mA mg(pd)(-1)) over previous reported PdCu alloy catalysts, and also much higher catalytic activity and durability comparing with Pd nanochains and commercial Pd/C. The catalytic enhancement mechanism to PdCu nanochains is proposed and discussed. Additionally, we found that the formation of PdCu nanochains follows a typical anisotropic growth approach, and the multiple steps of staged thermal treatment route displays a vital role in fabricating the unique PdCu nanochains while the introduced Cu precursors might affect the reduction rate of Pd species and act as deposition or nucleation sites for twisted structure in terms of rich twin boundaries. This work describes an efficient, low-Pd loading catalyst for electrooxidation of formic acid, and also demonstrates a universal method to fabricate other defect-rich catalysts for broad applications in energy conversion and storage systems and sensing devices. (C) 2018 Elsevier Inc. All rights reserved.