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Photo-electrochemical (PEC) devices allow for converting solar energy into chemical energy and for the production of energetically dense solar fuels. Light absorption, charge separation and transport, electrochemical reactions, and ionic transport are required in such devices, all processes happening simultaneously. PEC devices - compared to competing, conventional PV-electrolysis systems - offer the promise of less complexity in design and implementation and more flexibility in their use. Nevertheless, PEC devices' economic and performance competitiveness is not well understood, given their low technology readiness level. No study has considered accurate multi-physical, multi-scale, and multi-dimensional performance models, degradation aspects, and uncertainty in the performance and cost metrics. Addressing some of these unknowns and focusing on the conversion of solar energy into two different solar fuels (H2 from water and CO from CO2), the objective of this thesis is threefold: (i) conduct a system-level techno-economic analysis based on a systematic and physical performance model (including degradation), and address uncertainty via a probabilistic approach (Monte Carlo (MC) method); (ii) based on the insight gained from the techno-economic analysis, identify most promising design and operational principles, substantiated by experimental investigation of an example case to assess practical feasibility; and (iii) develop two intricate multi-dimensional, multi-physical models: one for an innovative PEC device designed to operate with water vapor, and the other for a PEC device utilizing concentrated solar light engaged in the conversion of CO2 to CO. Overall, this thesis provides a combination of experimental demonstration and simulation tools to conduct feasibility studies, predict costs, and provide design guidelines and operational conditions for PEC devices in diverse electrochemical processes. This scope extends the use of PEC devices beyond the traditional liquid water splitting reaction, encompassing applications such as water vapor splitting, energy storage, and CO2 reduction.

The semiconducting hybrid-organic inorganic halide perovskites have excellent optical and electronic properties that attract the interest of scientists and researchers. Perovskite solar cells have seen the most rising-rate in the chart of solar cell efficiency from 3 to over 25% in less than ten years. In the last three years, most researchers have been focusing on the α-FAPbI3-based perovskite solar cells due to having a lower bandgap (1.45 eV) which is closer to the Shockley-Queisser optimum (1.1- 1.4eV) to gain high efficiency. A distinctive feature of FAPbI3 is that it is more thermally stable compared to MAPbI3. However, the α-FAPbI3 perovskite is not stable at room temperature as it converts to the undesirable Ύ-phase. The 2D- Ruddlesden-Popper-phase-doped 3D FAPbI3 enhancing the stability of the structure, albeit the bandgap is increased rendering a less optimal bandgap. The main achievement of this thesis is discovering that the doping of FAPbI3 with large alkyl ammonium moieties enhances efficiency and stability while maintaining the bandgap of pure α-FAPbI3 perovskite phase. I describe the resulting composition by the formula (A)xFAPbI3, where A represents the large alkyl ammonium iodide species. I study the stabilization of α-FAPbI3 via doping with 5-amino valeric acid hydroiodide (AVAI). By using solid-state NMR, we demonstrate the atomic-level interaction between this molecular modulator and the perovskite lattice and propose a structural model of the stabilized three-dimensional structure, further aided by density functional theory (DFT) calculations. We find the presence of AVAI produces highly crystalline films with large, micrometer-sized grains and enhanced charge-carrier lifetimes, as probed by transient absorption spectroscopy. Optical measurements confirm that there is no effect on the bandgap of FAPbI3 after doping. The devices based on (AVAI)0.25FAPbI3 exhibit superior operational stability in comparison with neat FAPbI3 while achieving power conversion efficiency of 19%. A similar approach based on benzylammonium iodide (BzI) has been used. The structural and optical characterization of films based on (BzI)xFAPbI3 composition demonstrate that there is no 2D phase forming under these conditions. Moreover, solid-state NMR results show BzI interacting on the atomic level with α-FAPbI3 by binding to the 3D perovskite through hydrogen bonding interaction and stabilizing it against the detrimental α-to-Ύ phase transition. Perovskite solar cells based on the (BzI)0.25FAPbI3composition achieve power conversion efficiencies exceeding 20%, which is accompanied by enhanced shelf-life and operational stability, maintaining 80% of the performance after one year at ambient conditions. Finally, films based on (BzI)0.25FAPbI3 compositions are further investigated upon aging under the ambient conditions, as they show an unexpected transition from black to red color without transition to expected yellow Ύ phase, unlike the reference FAPbI3. I perform different measurements to investigate the nature of this red phase as a function of annealing temperature compare these properties to the corresponding Ruddlesden-Popper phase (Bz2FAn-1PbnI3n+1). The red phase was found to be a mixture of a 2D phase (n = 2) Bz2FAPb2I7 and Ύ-FAPbI3, which acts as a barrier to the α-to-Ύ phase transition.

Most households in sub-Saharan Africa rely on wood-based cooking fuels and their number is expected to rise. Despite this, national and subnational energy policies often neglect biomass cooking fuels. A Formative Scenario Analysis process is applied to show how the cooking fuel sector in Kilimanjaro Region (Tanzania) and Kitui County (Kenya) might evolve by 2030. In order to provide relevant knowledge for potential energy policies, this paper aims to identify the main drivers impacting the cooking fuel sector, and to assess and explore current and future demand and supply potential of biomass cooking fuels. Our results show that policies have the potential to substantially impact the future mix of cooking fuels and to foster or hamper the use of efficient cooking fuel technologies. Half of Kilimanjaro Region’s households could be supplied with biogas; in Kitui County, wood-based cooking fuels is likely to remain dominant but improving the efficiency of the technologies would reduce the demand for wood considerably. Hence, we argue that energy policies should explicitly consider biomass cooking fuels and endeavour to make this sector more sustainable and that priority should be given to increasing the sustainability of the biomass cooking fuel sector. Key leverage points to do so are improving the access to improved biomass technologies and capacity building.

The vulnerability of floodplain forests, a critically sensitive global ecosystem, is exacerbated by both hydrological management practices and the escalating frequency and severity of drought events caused by climate change. This issue is particularly acute in Central European floodplain forests, where river regulation and reduced groundwater levels have markedly contributed to increased water deficits and intensified drought conditions, causing forest growth decline, species dieback and shifts in forest composition. In this study, we utilized tree-ring measurements from pedunculate oak (Quercus robur L.) and narrow-leaved ash (Fraxinus angustifolia Vahl.) across four sites with varying groundwater levels. This approach allowed us to assess the impact of artificial groundwater modifications and drought conditions in their growth, providing valuable insights into the resilience and adaptation of these species. Our study indicates that the most determining drivers of tree-growth are hydrological parameters such as groundwater levels and drought indices while temperature alone was less important for tree growth. However, we observed species-specific growth responses to these environmental drivers. In particular, Q. robur exhibited a greater adaptability to climatic variables, with a weaker relationship of tree-ring width to climate compared to F. angustifolia, which demonstrated a stronger dependence on hydroclimatic variables and appeared to feature a higher drought susceptibility. Our findings also reveal that radial growth during the vegetation period relies on different water sources - in spring, growth is primarily driven by precipitation, while groundwater levels become more critical in summer and autumn. Overall, our study underscores the significant threat posed to floodplain forests by both groundwater modifications and the escalating frequency of drought events. However, not all floodplain species are equally adaptable to these environmental changes, exhibiting varied responses and vulnerability.

The most extreme environments are the most vulnerable to transformation under a rapidly changing climate. These ecosystems harbor some of the most specialized species, which will likely suffer the highest extinction rates. We document the steepest temperature increase (2010-2021) on record at altitudes of above 4,000 m, triggering a decline of the relictual and highly adapted moss Takakia lepidozioides. Its de-novo-sequenced genome with 27,467 protein-coding genes includes distinct adaptations to abiotic stresses and comprises the largest number of fast-evolving genes under positive selection. The uplift of the study site in the last 65 million years has resulted in life-threatening UV-B radiation and drastically reduced temperatures, and we detected several of the molecular adaptations of Takakia to these environmental changes. Surprisingly, specific morphological features likely occurred earlier than 165 mya in much warmer environments. Following nearly 400 million years of evolution and resilience, this species is now facing extinction.

Earth’s biodiversity and human societies face pollution, overconsumption of natural resources, urbanization, demographic shifts, social and economic inequalities, and habitat loss, many of which are exacerbated by climate change. Here, we review links among climate, biodiversity, and society and develop a roadmap toward sustainability. These include limiting warming to 1.5°C and effectively conserving and restoring functional ecosystems on 30 to 50% of land, freshwater, and ocean “scapes.” We envision a mosaic of interconnected protected and shared spaces, including intensively used spaces, to strengthen self-sustaining biodiversity, the capacity of people and nature to adapt to and mitigate climate change, and nature’s contributions to people. Fostering interlinked human, ecosystem, and planetary health for a livable future urgently requires bold implementation of transformative policy interventions through interconnected institutions, governance, and social systems from local to global levels.