b S Supporting Information ' INTRODUCTIONSynthesis and properties of functional branched and star polymers have attracted much attention since these polymers usually possess unique physicochemical properties and wide applications originating from a large number of chain ends per molecule and their branched chain architectures. Generally, hyperbranched polymers can be synthesized by step-growth polymerization via polycondensation or addition polymerization of multifunctional monomers, 3,4,30-32 copolymerization of conventional monomers via self-condensing vinyl polymerization (SCVP), 33-37 or copolymerization of vinyl monomers in the presence of multifunctional vinyl comonomers. 38,39 "Living"/ controlled radical polymerization approaches such as inifertermediated polymerization, 40 nitroxide-mediated polymerization, 41 atom transfer radical polymerization, 42-44 and reversible addition-fragmentation chain transfer (RAFT) polymerization [45][46][47][48][49][50][51][52][53] have been efficiently used to synthesize a variety of hyperbranched and star polymers with controlled compositions and variable functionality. Among them, RAFT polymerization is a facile and versatile approach to synthesize hyperbranched and star polymers due to its many advantages such as relatively mild reactions, wide range of monomers, tolerance of various functionalities, and lack of metal catalyst. A range of hyperbranched polymers have been achieved by RAFT polymerization in the presence of divinyl comonomers, 38,39 from a polymer backbone with pendant xanthate groups, 54 or with AB* styryl or acryloyl chain transfer agents. 55-58 Until now, the types of hyperbranched polymers obtained via RAFT process were relatively limited, and the feed ratio of vinyl monomer to chain transfer agent was usually higher than 10. In particular, the copolymerization behavior of conventional monomer with polymerizable RAFT agent has not been thoroughly investigated. It is therefore of great interest to study in depth the dependence of copolymer composition and degree of branching (DB) of hyperbranched copolymers on reaction conditions during RAFT polymerization.Star polymers, on the other hand, have been well-studied. They can be synthesized by approaches such as "arm first", 59-63 "core first", 64-67 and their combination. [68][69][70][71] The arm first approach involves the synthesis of prefabricated arms, usually through "living"/controlled polymerization, followed by reaction with a multifunctional core reagent, which is easily performed and can also afford target star polymers with low polydispersity. The potential drawback of arm first method is that the arm ABSTRACT: Facile synthesis of hyperbranched and star polymers on the basis of S-(4-vinyl)benzyl S 0 -propyltrithiocarbonate (VBPT) was described. RAFT copolymerization of VBPT with vinyl monomers such as methyl methacrylates (MMA), styrene (St), methyl acrylate (MA), and tert-butyl acrylate (tBA) afforded hyperbranched copolymers with variable branch length and degree of branching. Hyperbranched ...

Bifunctional hydrogen electrocatalysis (hydrogen‐oxidation and hydrogen‐evolution reactions) in alkaline solution is desirable but challenging. Among all available electrocatalysts, Ni‐based materials are the only non‐precious‐metal‐based candidates for alkaline hydrogen oxidation, but they generally suffer from low activity. Here, we demonstrate that properly alloying Ni with Mo could significantly promote its electrocatalytic performance. Ni4Mo alloy nanoparticles are prepared from the reduction of molybdate‐intercalated Ni(OH)2 nanosheets. The final product exhibits an apparent hydrogen‐oxidation activity exceeding that of the Pt benchmark and a record‐high mass‐specific kinetic current of 79 A g−1 at an overpotential of 50 mV. A superior hydrogen‐evolution performance is also measured in alkaline solution. These experimental data are rationalized by our theoretical simulations, which show that alloying Ni with Mo significantly weakens its hydrogen adsorption, improves the hydroxyl adsorption and decreases the reaction barrier for water formation.

Palladium is a promising material for electrochemical CO 2 reduction to formate with high Faradaic efficiency near the equilibrium potential. It unfortunately suffers from problematic operation stability due to the CO poisoning on surface. Here, we demonstrate that alloying is an effective strategy to alleviate this problem. Mesoporous PdAg nanospheres with uniform size and composition are prepared from the co-reduction of palladium and silver precursors in aqueous solution using dioctadecyldimethylammonium chloride as the structure directing agent. The best candidate can initiate CO 2 reduction at zero overpotential, and achieve high formate selectivity close to 100% and great stability even at <-0.2 V versus reversible hydrogen electrode. The high selectivity and stability are believed to result from the electronic coupling between Pd and Ag, which lowers the d-band center of Pd and thereby significantly enhances its CO tolerance, as evidenced by both electrochemical analysis and theoretical simulations.

Palladium can enable the electrochemical CO2 reduction to formate with nearly zero overpotential and good selectivity. However, it usually has very limited stability owing to CO poisoning from the side reaction intermediate. Herein, it is demonstrated that alloying palladium with silver is a viable strategy to significantly enhance the electrocatalytic stability. Palladium–silver alloy nanowires are prepared in aqueous solution with tunable chemical compositions, large aspect ratio, and roughened surfaces. Thanks to the unique synergy between palladium and silver, these nanowires exhibit outstanding electrocatalytic performances for selective formate production. Most remarkably, impressive long‐term stability is measured even at < ‐0.4 V versus reversible hydrogen electrode where people previously believed that formate cannot be stably formed on palladium. Such stability results from the enhanced CO tolerance and selective stabilization of key reaction intermediates on alloy nanowires as supported by detailed electrochemical characterizations and theoretical computations.

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