The production of fuels from sunlight represents one of the major challenges to the development of a sustainable energy system [1-5]. Hydrogen is the simplest fuel to produce and while platinum and other noble metals are efficient catalysts for photoelectrochemical hydrogen evolution [6-9], earth-abundant alternatives are needed for large-scale use [10-15]. We show that bioinspired molecular clusters based on molybdenum and sulfur evolve hydrogen at rates comparable to that of platinum [6]. The incomplete cubane-like clusters (Mo 3 S 4 ) efficiently catalyze the evolution of hydrogen when coupled to a p-type Si semiconductor that harvests red photons in the solar spectrum. The current densities at the reversible potential match the requirement of a photoelectrochemical hydrogen production system with a solar-tohydrogen efficiency in excess of 10% [16]. The experimental observations are supported by DFT calculations of the Mo 3 S 4 cluster adsorbed on the hydrogen-terminated Si(100) surface providing insights into the nature of the active site.

Ireland has an abundant supply of renewable energy, a dangerous reliance on imported fossil fuels, as well as very demanding energy and CO 2 targets to reach. All of these indicate that a major alternation to the current energy system is necessary, especially an increase in the utilisation of renewable energy. Consequently, this study presents the first step towards identifying how this transition may be achieved for the Republic of Ireland. The energysystems-analysis tool, EnergyPLAN, was chosen for this investigation, as it accounts for all sectors that need to be considered for integrating large penetrations of renewable energy: the electricity, heat and transport sectors. Initially, a reference model of the existing Irish energysystem was constructed, and subsequently alternatives were compared to identify the most effective method of increasing renewable energy penetration. The results in this paper illustrate the four scenarios of a 100% renewable energy system for Ireland: a biomass, hydrogen, electricity and combination scenario. However, these results have been completed based on numerous assumptions that will need to be investigated in future work, before a serious roadmap can be defined for Ireland's renewable energy transition. * Corresponding author 1 Ireland refers to the Republic of Ireland only unless otherwise specified.

This study, called APEX, is exploring novel concepts for fusion chamber technology that can substantially improve the attractiveness of fusion energy systems. The emphasis of the study is on fundamental understanding and advancing the underlying engineering sciences, integration of the physics and engineering requirements, and enhancing innovation for the chamber technology components surrounding the plasma. The chamber technology goals in APEX include: (1) high power density capability with neutron wall load \ 10 MW/m 2 and surface heat flux \ 2 MW/m 2 , (2) high power conversion efficiency ( \ 40%), (3) high availability, and (4) simple technological and material constraints. Two classes of innovative concepts have emerged that offer great promise and deserve further research and development. The first class seeks to eliminate the solid ''bare'' first wall by flowing liquids facing the plasma. This liquid wall idea evolved during the APEX study into a number of concepts based on: (a) using liquid metals (Li or Sn-Li) or a molten salt (Flibe) as the working liquid, (b) utilizing electromagnetic, inertial and/or other types of forces to restrain the liquid against a backing wall and control the hydrodynamic flow configurations, and (c) employing a thin ( 2 cm) or thick ( 40 cm) liquid layer to remove the surface heat flux and attenuate the neutrons. These liquid wall concepts have some common features but also have widely different issues and merits. Some of the attractive features of liquid walls include the potential for: (1) high power density capability; (2) higher plasma b and stable physics regimes if liquid metals are used; (3) increased disruption survivability; (4) reduced volume of radioactive waste; (5) reduced radiation damage in structural materials; and (6) higher availability. Analyses show that not all of these potential advantages may be realized simultaneously in a single concept. However, the realization of only a subset of these advantages will result in remarkable progress toward attractive fusion energy systems. Of the many scientific and engineering issues for liquid walls, the most important are: (1) plasma-liquid interactions including both plasma-liquid surface and liquid wall-bulk plasma interactions; (2) hydrodynamic flow configuration control in complex geometries including penetrations; and (3) heat transfer at free surface and temperature control. The second class of concepts focuses on ideas for extending the capabilities, particularly the power density and operating temperature limits, of solid first walls. The most promising idea, called EVOLVE, is based on the use of a high-temperature refractory alloy (e.g. W -5% Re) with an innovative cooling scheme based on the use of the heat of vaporization of lithium. Calculations show that an evaporative system with Li at 1 200°C can remove the goal heat loads and result in a high power conversion efficiency. The vapor operating pressure is low, resulting in a very low operating stress in the structure. In addition, the lithium flow rate is about a factor of ten lower than that required for traditional self-cooled first wall/blanket concepts. Therefore, insulator coatings are not required. Key issues for EVOLVE include: (1) two-phase heat transfer and transport including MHD effects; (2) feasibility of fabricating entire blanket segments of W alloys; and (3) the effect of neutron irradiation on W.