Climate change caused by anthropogenic greenhouse gas emissions necessitates a transition from fossil resources to greener fuels and chemicals. Hydrogen is a promising green energy vector due to its high gravimetric energy density, its potential use in fuel cells to generate power with only water as an emission and its water splitting, or electrolysis, production method which results in green hydrogen when powered by renewable energy. Currently, however, only 4% of hydrogen is produced using electrolysis, with the rest coming almost exclusively through fossil fuel reforming. The state-of-the-art commercial electrolysis systems are based on alkaline electrolysis (AEL), which has low system efficiency of around 60% and a low tolerance to the fluctuations in power input inherent to intermittent renewable energies such as solar and wind. The next generation of electrolysers, namely proton exchange membrane electrolysis (PEMEL), have lower system resistance and are therefore predicted to achieve efficiencies of 80 – 90%. PEMEL also have significantly higher tolerance to power fluctuations, allowing them to address some of the challenges of AEL. However, PEMEL is only expected to become cost competitive with AEL in 2030 due to its use of expensive and rare elements, especially in (i). the hydrogen evolution reaction (HER) catalyst with the state-of-the-art being Pt, (ii). the oxygen evolution reaction (OER) catalyst with the state-of-the-art being Ir, (iii). precious metal (Pt, Au) coatings on gas diffusion electrode (GDE) and iv. the perfluorosulfonic acid-based membrane. The following work aims to develop HER and OER catalysts, and GDEs for water-splitting based on cheap and abundant materials. Chapters two and three focus on the improvement of performance and stability of molybdenum sulfide HER catalysts through bio-inspired iron doping and polymer encapsulation, respectively. The iron doped catalyst was deposited on a carbon nanotube network , leading to a significant enhancement in performance, resulting in a notable 1 A cm-2 at 1.85 V when tested in a prototype electrolyser set-up in combination with a state-of the-art electrode. The polymer encapsulation is shown to improve the stability of molybdenum sulfide in the presence of oxygen and achieves a similar performance of 1 A cm-2. The fourth chapter discusses appropriate and novel GDEs for precious metal free oxygen evolution focussing on manganese oxide based OER catalysts as a case study. Fluorine-doped tin oxide coated quartz felt has been found to be a highly stable support suitable for testing even low performance OER catalysts. In chapter five, the lifecycle assessment and techno-economic study of two promising precious metal-free catalysts are discussed, which demonstrate the significantly lower environmental impact and cost of the precious metal free catalysts in the manufacturing phase, however their performance should be improved to compensate for the additional power consumption in the operation phase. Finally, chapter six explores direct solar to hydrogen conversion through photoelectrochemical methods, where monolayer nanoflakes of semiconducting molybdenum disulfide are re-stacked using conductive ligands, resulting in a 50% higher photocurrent density for a ligand-bound sample compared to the reference material.