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The lifetime and reliability of power transformers are primarily dependent on the hot-spot temperature in the windings, as temperature is the most important factor determining the insulation degradation rate. Key to removing the heat from the transformer is the radiator which must be carefully designed to keep the temperatures within limits under all operating conditions whilst minimizing the transformer size, weight and cost. This paper compares the analytical method used to predict the radiator performance with computational fluid dynamics (CFD) models in terms of heat dissipation. It is found that the analytical method and CFD models give similar results in the air natural (AN) cooling modes, whereas the analytical method overestimates the heat dissipation in the air forced (AF) cooling modes. Moreover, the thermal conduction effect in the radiator wall is investigated under different operating conditions and for different radiator sizes using the CFD models. The simulation results indicate that the radiator wall contributes to 6%-10% of the total heat dissipation under some circumstances and therefore should not be simply ignored in radiator models.

Organic solar cells utilize an energy-level offset to generate free charge carriers. Although a very small energy-level offset increases the open-circuit voltage, it remains unclear how exactly charge generation is affected. Here we investigate organic solar cell blends with highest occupied molecular orbital energy-level offsets (∆EHOMO) between the donor and acceptor that range from 0 to 300 meV. We demonstrate that exciton quenching at a negligible ∆EHOMO takes place on timescales that approach the exciton lifetime of the pristine materials, which drastically limits the external quantum efficiency. We quantitatively describe this finding via the Boltzmann stationary-state equilibrium between charge-transfer states and excitons and further reveal a long exciton lifetime to be decisive in maintaining an efficient charge generation at a negligible ∆EHOMO. Moreover, the Boltzmann equilibrium quantitatively describes the major reduction in non-radiative voltage losses at a very small ∆EHOMO. Ultimately, highly luminescent near-infrared emitters with very long exciton lifetimes are suggested to enable highly efficient organic solar cells. Donor–acceptor systems with low energy-level offset enable high power efficiency in organic solar cells yet it is unclear what drives charge generation. Classen et al. show that long exciton lifetimes enable efficient exciton splitting and thus generation of free charges while also suppressing voltage losses.

Seaweed fibre is usually discarded as biomass waste after extraction of useful ingredients from seaweed. However this seaweed fibre, a natural abundant cellulose material with uniform dimensions 10 times smaller than other plant-based fibre can be utilized as electrode material for energy storage. In this work, we converted seaweed fibre into conductive carbon electrodes by a thermal carbonisation method. The morphology, chemical composition and conductivity are highly influenced by the carbonisation temperature. In comparison to other biomass sources such as cotton pulp, seaweed fibre is finer, smoother and more conductive at low carbonisation temperature. These carbonized seaweeds were then used as a supercapacitor, giving a high supercapacitance (226.3 Fg−1) at the carbonisation temperature of 900°C, and good stability within 2400 cycles. This specific capacitance is significantly higher than values obtained from filter paper or cotton pulp.

The optical and photovoltaic properties of Si NCs / SiC multilayers (MLs) are investigated using a membrane-based solar cell structure. By removing the Si substrate in the active cell area, the MLs are studied without any bulk Si substrate contribution. The occurrence is confirmed by scanning electron microscopy and light-beam induced current mapping . Optical characterization combined with simulations allows us to determine the absorption within the ML absorber layer, isolated from the other cell stack layers. The results indicate that the absorption at wavelengths longer than 800 nm is only due to the SiC matrix. The measured short-circuit current is significantly lower than that theoretically obtained from absorption within the ML absorber, which is ascribed to losses that limit carrier extraction. The origin of these losses is discussed in terms of the material regions where recombination takes place. Our results indicate that carrier extraction is most efficient from the Si NCs themselves, whereas recombination is strongest in SiC and residual a-Si domains . Together with the observed onset of the external quantum efficiency (EQE) at 700-800 nm, this fact is an evidence of quantum confinement in Si NCs embedded in SiC on device level.

The aggravating global problems of energy crisis, rising atmospheric greenhouse gas concentrations and accumulation of persistent waste have attracted the attention of scientists, policy-makers and global organisations to come up with effective and expeditious solutions to address these challenges. In this context, the development of sustainable technologies driven by renewable energy sources for the production of clean fuels and commodity chemicals from diverse waste feedstocks is an appealing approach towards creating a circular economy. Over the years, semiconductor photocatalysts based on TiO₂, CdS, carbon-nitrides (CNx) and carbon dots (CDs) have been widely used for the photocatalytic reforming (PC reforming) of pre-treated waste substrates to organic products, accompanied with clean hydrogen (H₂) generation. However, these conventional solar-driven processes suffer from major drawbacks such as low production rates, poor product selectivity, CO₂ release, challenging process and catalyst optimisation, and harsh waste pre-treatment conditions, which limit their commercial applicability. These challenges are tackled in this thesis with the introduction of new and efficient photoelectrochemical (PEC) and chemoenzymatic processes for reforming a diverse range of waste feedstocks to sustainable fuels. Solar-driven PEC reforming based on halide perovskite light-absorber is first developed as an attractive alternative to PC reforming. The PEC systems consist of a perovskite|Pt photocathode for clean H₂ production and a Cu-Pd alloy anode for reforming diverse waste streams, including pre-treated cellulosic biomass, polyethylene terephthalate (PET) plastics, and industrial by-product glycerol into industrially-relevant, value-added chemicals (gluconic acid, glycolic acid and glyceric acid) without any externally applied bias or voltage. Additionally, the single light-absorber PEC systems can also convert the airborne waste stream and greenhouse gas CO₂ to diverse products with the simultaneous reforming of PET plastics with no applied voltage. The perovskite-based photocathode enables the integration of different CO₂ reduction catalysts such as a molecular cobalt porphyrin, a Cu-In alloy and formate dehydrogenase enzyme, which produce CO, syngas and formate, respectively. The versatile PEC systems, which can be assembled in either a ‘two-compartment’ or standalone ‘artificial leaf’ configurations achieve 60‒90% oxidation product selectivity (with no over-oxidation) and >100 µmol cm‾² h‾¹ product formation rates, corresponding to 10²‒10⁴ times higher activity than conventional PC reforming systems. In addition to developing PEC platforms, this thesis also explores avenues for circumventing the harsh alkaline pre-treatment strategies (pH >13, 60‒80 ºC) adopted for photoreforming waste substrates. For this purpose, a chemoenzymatic pathway is introduced whereby PET and polycaprolactone plastics were deconstructed using functional enzymes under benign conditions (pH 6‒8, 37‒65 ºC), followed by PC reforming using Pt loaded TiO₂ (TiO₂|Pt) or Ni₂P loaded carbon-nitride (CNx|Ni₂P) photocatalysts. The chemoenzymatic reforming process demonstrates versatility in upcycling polyester films and nanoplastics for H₂ production at high yields reaching ∼10³‒10⁴ µmol gsub‾¹ and activities at >500 µmol gcat‾¹ h‾¹. The utilisation of enzyme pre-treated plastics also allowed the coupling of plastic reforming with photocatalytic CO₂-to-syngas conversion using a phosphonated cobalt bis(terpyridine) co-catalyst immobilised on TiO₂ (TiO₂|CotpyP). Finally, moving beyond solar-driven systems, a bio-electrocatalytic flow process is demonstrated for the conversion of microbe pre-treated food waste to ethylene (an important feedstock in the chemical industry) on graphitic carbon electrodes via succinic acid as the central intermediate. In conclusion, with its focus on improving efficiencies, achieving selective product formation, building versatile platforms, diversifying substrate and product scope, and reducing carbon footprint and economic strain, this thesis aims to bring sustainable waste-to-fuel technologies a step closer to commercial implementation.

Revolutionary catalyst protection by single layer graphene capping, tremendous catalyst lifetime longevity and activity enhancement towards oxygen reduction reaction.

National net zero emission targets could, if fully implemented, reduce best estimates of projected global average temperature increase to 2.0–2.4 °C by 2100, bringing the Paris Agreement temperature goal within reach. A total of 131 countries are discussing, have announced or have adopted net zero targets, covering 72% of global emissions. These targets could substantially lower projected warming as compared to currently implemented policies (2.9–3.2 °C) or pledges submitted to the Paris Agreement (2.4–2.9 °C). Current pledges for emissions cuts are insufficient to meet the Paris Agreement temperature goal. The wave of net zero targets being discussed and adopted could make the Paris goal possible if further countries follow suit.