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Recent progress in the development of a new class of inexpensive metal-free and non-noble metal-based electrocatalysts for the cathodic reduction of oxygen is discussed.

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Synthesis of non-Pt bifunctional electrocatalyst for the anodic oxidation of liquid fuel and cathodic reduction of oxygen is of great interest in the development of energy conversion devices. We demonstrate a facile room-temperature synthesis of surface-engineered trimetallic alloy nanoelectrocatalyst based on Co, Cu, and Pd by thermodynamically favorable transmetallation reaction and electrochemical dealloying. The quasi-spherical Co x Cu y Pd z trimetallic catalysts were synthesized by the thermodynamically favorable reaction of K 2 PdCl 4 with sheetlike Co m Cu n bimetallic alloy nanostructure. The surface engineering of Co x Cu y Pd z was achieved by electrochemical dealloying. The surface-engineered alloy electrocatalyst exhibits excellent bifunctional activity toward formic acid oxidation reaction (FAOR) and oxygen reduction reaction (ORR) at same pH. The elemental composition and lattice strain control the electrocatalytic performance. The elemental composition-dependent compressive strain weakens the adsorption of oxygen-containing species and favors the facile electron transfer for FAOR and ORR. The engineered alloy electrocatalyst of Co 0.02 Cu 13.8 Pd 86.18 composition is highly durable and delivers high mass-specific activity for ORR and FAOR. It delivers mass-specific activities of 1.50 and 0.202 A/mg Pd for FAOR and ORR, respectively, in acidic pH. The overall performance is superior to that of as-synthesized Pd and dealloyed bimetallic Co 2.7 Pd 97.3 and Cu 5.61 Pd 94.39 nanoelectrocatalysts.

Structurally ordered intermetallic compounds are proven to be very promising for electrocatalysis owing to the homogeneous distribution of active sites, thermodynamic stability, and resistance toward surface rearrangement. Herein, we demonstrate a facile route for the synthesis of Sn-and Pd-based ordered intermetallics hybridized with reduced graphene oxide (rGO) and their bifunctional electrocatalytic performance toward oxygen reduction (ORR) and ethylene glycol oxidation reactions (EGOR). The coreduction of SnCl 2 and K 2 PdCl 4 in 1,5pentanediol in the presence of graphene oxide and the subsequent thermal annealing in an inert atmosphere affords rGO hybridized intermetallics of three phases: primitive orthorhombic PdSn, base-centered orthorhombic PdSn 2 , and hexagonal Pd 3 Sn 2 . The electrocatalytic performance of the hybrid intermetallics toward EGOR and ORR is evaluated in alkaline and acidic electrolytes. Among the three intermetallics, PdSn has excellent electrocatalytic performance toward EGOR and ORR. The PdSn/rGO hybrid catalyst outperforms the other two intermetallics toward EGOR in alkaline pH and ORR in acidic as well as alkaline pH in terms of onset potential and mass specific activity. The enhanced performance of PdSn/rGO catalyst is attributed to (i) a change in the Pd dband center, (ii) a Pd−Pd interatomic distance in a unit cell, and (iii) weak adsorption of in-situ-generated oxygen-containing intermediates species. The lattice strain due to the presence of dissimilarly sized Sn and Pd in a unit cell and the high oxophilicity of Sn downshifts the d-band center of Pd and facilitate the electron transfer kinetics. The catalyst support, rGO, prevents the unwanted aggregation of the active catalyst. The density functional theory calculations show that the oxygen-containing species weakly adsorb on the PdSn surface compared to the other intermetallics, supporting the high electrocatalytic activity of PdSn/rGO.