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We use experimental and computational studies of core–shell metal–semiconductor and metal–molecule systems to investigate the mechanism of energy flow and energetic charge carrier generation in multicomponent plasmonic systems. We demonstrate that the rates of plasmon decay through the formation of energetic charge carriers are governed by two factors: (1) the intensity of the local plasmon induced electric fields at a specific location in the multicomponent nanostructure, and (2) the availability of direct, momentum conserved electronic excitations in the material located in that specific location. We propose a unifying physical framework that describes the flow of energy in all multicomponent plasmonic systems and leads us towards molecular control of the energy flow and excited charge carrier generation in these systems. 

The materials that are receiving the most attention in photoelectrochemical water splitting are metallic nanoparticle electrocatalysts (np‐EC) attached to the surface of a semiconductor (SC) light absorber. In these multicomponent systems, the interface between the semiconductor and electrocatalysts critically affects performance. However, the np‐EC/SC interface remains poorly understood as it is complex on atomic scales, dynamic under reaction conditions, and inaccessible to direct experimental probes. This contribution sheds light on how the electrocatalyst/semiconductor interface evolves under reaction conditions by investigating the behavior of nickel electrocatalysts (as nanoparticles and films) deposited on silicon semiconductors. Rigorous electrochemical experiments, interfacial atomistic characterization, and computational modeling are combined to demonstrate critical links between the atomistic features of the interface and the overall performance. It is shown that electrolyte‐induced atomistic changes to the interface lead to (1) modulation of the charge carrier fluxes and a dramatic decrease in the electron/hole recombination rates and (2) a change in the barrier height of the interface. Furthermore, the critical roles of nonidealities and electrocatalyst coverage due to interfacial geometry are explored. Each of these factors must be considered to optimize the design of metal/semiconductor interfaces which are broadly applicable to photoelectrocatalysis and photovoltaic research.