The selection of a reaction pathway with high energy barrier in a multipath on-surface reaction system has been challenging. Herein, we report the successful control of the reaction system of 1,1′-biphenyl-4-bromo-4′-ethynyl (BPBE) on Ag(111), in which three coupling reactions (Glaser, Ullman, Sonogashira) are involved. Either graphdiyne (GDY) or graphyne (GY) nanowires can be formed by distinct kinetic strategies. As the energetically favorable pathway, the formation of a GDY nanowire is achieved by hierarchical activation of Glaser (with lowest energy barrier) and Ullman coupling of BPBE. On the other hand, the formation of a GY nanowire originates from the high selectivity of the high-barrier Sonogashira coupling, whose indispensable kinetic parameters are high surface temperature, low molecular coverage, and low precursor evaporation rate, as derived from a series of control experiments. This work achieves the fabrication of GY nanowires via on-surface Sonogashira coupling for the first time and reveals mechanistic control strategies for potential syntheses of other functional nanostructures via cross-couplings on surfaces.

The mechanisms of Glaser coupling reaction on metal surfaces have been poorly understood. Herein, we propose a reaction pathway toward surface-confined Glaser coupling which is initiated by single-molecule dehydrogenation of terminal alkyne. This is inspired by our experimental observations of alkynyl–Ag–alkynyl and alkynyl–Cu–alkynyl type organometallic intermediates in the coupling reaction of 1,1′-biphenyl,4-bromo-4′-ethynyl (BPBE) on Ag(111) and Cu(111), respectively. Theoretical calculations reveal that the dehydrogenation process of terminal ethynyl of BPBE is most likely catalyzed by a stray H adatom on Ag(111) but by a Cu adatom on Cu(111), followed by the formation of the organometallic intermediates. After the release of interstitial metal adatoms, the final C–C coupling occurs easily on Ag(111) but shows extremely low efficiency on Cu(111), due to the too strong interaction between ethynylene and the Cu(111) substrate.

evolution reaction (HER) and anodic oxygen evolution reaction (OER) require abundant, cheap, stable, and efficient electrocatalysts. In the past years, huge efforts have been devoted to the development of low-cost electrocatalysts based on transition metals. In general, transition metals, [4] and their nitrides, [5] phosphides, [6] and sulfides, [7] exhibit effective catalytic activity for HER in pH-universal electrolytes, while metallic oxides, [8] and hydroxides, [9] are predominantly alkaline OER electrocatalysts. Nevertheless, it is still difficult to integrate HER and OER in a common electrolyzer due to that most OER electrocatalysts are inactive or corroded in acid media. [10] In this regard, it is crucial to develop cost-effective bifunctional electrocatalysts toward both HER and OER in alkaline media. Up to date, numerous bifunctional electrocatalysts composed of two or more active components have been designed and prepared via interfacial engineering, such as metal-semiconductor Mott-Schottky heterojunctions, [11] heterogeneous sulfides, [12] and phosphides hybrids. [13] These heterogeneous electrocatalysts usually possess the advantages of each component and exhibit vastly improved electrocatalytic performance because of the modified electronic structure in the vicinity of interfaces.Whereas, how to design and synthesize heterogeneous bifunctional electrocatalysts is still lacking systematic reports. Recently, it has been demonstrated that n-type semiconductor catalysts favor cathodic HER and p-type ones prefer anodic OER. [14] On account of this view, it is envisaged that integrating an n-type semiconductor and a p-type one would bring about bifunctional HER and OER electrocatalyst. As is well known, upon intimate contact of p-type and n-type semiconductors to form p-n junction, their Fermi levels turn to be aligned, leading to the formation of the opposite space-charge region at the interface. [15] This changed electronic structure has a great influence on the absorption of target ions and the charge transfer during electrochemical reactions. [16] Specifically, the positively charged n-type side is in favor of the absorption of OH − ions to facilitate OER. [17] Though it has been concluded that the enriched electron density on a metal surface could lead to the stabilization of adsorbed hydrogen for enhanced HER, [18] how the negatively charged p-type side affects HER is still unknown. Heterostructure plays an important role in boostingthe overall water splitting (OWS) performance of nonprecious metal electrocatalysts. However, rational design and synthesis of semiconductor heterojunctions especially for Cu-based ones as efficient bifunctional electrocatalysts toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) still face challenges, and the in-depth study of catalytic mechanisms is urgently needed. Herein, n-type cobalt layered double hydroxide nanosheets are assembled on p-type cuprous phosphide nanowire to form p-n junction. This heterostructure with a strong built-in potent...