http://theses.ncl.ac.uk/jspui/handle/10443/73 Sat, 02 May 2026 04:40:36 GMT 2026-05-02T04:40:36Z http://theses.ncl.ac.uk/jspui/handle/10443/6746 Title: A novel transition metal dichalcogenide – reduced graphene oxide electrocatalyst family for hydrogen evolution reaction Authors: Jiang, Jianan Abstract: The global energy crisis underscores the critical need for sustainable hydrogen production via efficient electrocatalysts. This study presents a novel family of transition metal dichalcogenide-reduced graphene oxide (MoS2-rGO) hybrids and doped variants (V, W, Co) for the hydrogen evolution reaction (HER). Using orthogonal experimental design (L9(33)), we optimized synthesis parameters (rGO content, heating temperature, duration) to develop a MoS2-rGO composite with 0.8 wt% rGO, synthesized at 200°C for 24 h. This optimized catalyst achieved superior HER performance in acidic media (0.5 M H2SO4), exhibiting a low overpotential (η10 = -0.34 Vs RHE) and Tafel slope (98.2 mV/dec), significantly outperforming undoped MoS2 (η10 > 0.40 Vs RHE, Tafel slope 113.0 mV/dec). While Pt/C remains the benchmark catalyst with ultra-low overpotential (~0.05 V vs. RHE) and a Tafel slope of ~30 mV/dec, its high cost and scarcity hinder widespread application. In contrast, our MoS2-rGO catalysts offer a noble-metal-free alternative with enhanced conductivity and stability, facilitated by rGO integration. XRD and Raman spectroscopy confirmed structural improvements, while vanadium doping increased active site exposure, tungsten doping introduced sulfur vacancies to optimize hydrogen adsorption energy, and cobalt doping altered electronic structures. Systematic characterization via XRD, XPS, BET, UV-vis, Raman spectroscopy, SEM and electrochemical techniques elucidated the structural and electronic contributions of each component. The synergistic effects of rGO and dopants were highlighted, with the Co0.05W0.05S2/rGO heterostructure showing promising HER activity. This work establishes a rational framework for designing noble-metal-free HER catalysts, emphasizing the interplay between defect engineering, interfacial interactions, and scalable synthesis strategies. The integration of orthogonal optimization with multi-technique characterization provides a robust pathway for advancing green hydrogen technologies. Description: Ph. D. Thesis. Wed, 01 Jan 2025 00:00:00 GMT http://theses.ncl.ac.uk/jspui/handle/10443/6746 2025-01-01T00:00:00Z http://theses.ncl.ac.uk/jspui/handle/10443/6744 Title: Bayesian inference on the order of stationary vector autoregressions with application to multivariate modelling of electroencephalography data Authors: Binks, Rachel Louise Abstract: Vector autoregressions (VARs) are widely used for modelling multivariate time series. VARs have an associated order p; given observations at the preceding p time points, the variable at time t is conditionally independent of all earlier history. The model order is therefore intrinsic to the characterisation of the process. It is common to assume a VAR is stationary, which requires the means, variances and covariances of the process to be constant over time. This can be enforced by imposing the stationarity condition which restricts the parameter space of the autoregressive coefficients to the stationary region. However, implementing this constraint is difficult as the stationary region has a complex geometry. Fortunately, pioneering recent work has provided a solution for enforcing stationarity in autoregressions of fixed order p based on a reparameterisation in terms of a set of interpretable and unconstrained transformed partial autocorrelation matrices. In this research, focus is placed on the difficult problem of allowing p to be unknown, developing priors and computational inference that take full account of order uncertainty. To this end, a comparison of existing approaches for determining the order of station ary univariate autoregressions is provided. An approach employing shrinkage priors for partial autocorrelations is then generalised for the multivariate case, using the cumula tive shrinkage and multiplicative gamma process priors to increasingly shrink the partial autocorrelation matrices with increasing lag. Identifying the lag beyond which these ma trices become equal to zero then determines p. Methods for identifying whether a partial autocorrelation matrix is effectively zero are developed. The work is illustrated through application to neural activity data. In particular, a detailed discussion of methods to decompose a VAR into latent processes is provided, which is then used to investigate ultradian rhythms in the brain. Relationships between different regions of the brain are investigated through Granger causality plots. Description: PhD Thesis Wed, 01 Jan 2025 00:00:00 GMT http://theses.ncl.ac.uk/jspui/handle/10443/6744 2025-01-01T00:00:00Z http://theses.ncl.ac.uk/jspui/handle/10443/6743 Title: Characterisation of geological storage on the UKCS from interpretation of seismic reflection data Authors: Barnett, Hector George Abstract: This thesis investigates the impact of interpretation uncertainty on subsurface storage sites for the purposes of storing either hydrogen or carbon dioxide. 3D seismic and well data were used alongside complementary modelling methods to quantify uncertainties and sensitivities. The work investigates three themes, the interpretation of the complex internal structure of evaporites; the impact of geological uncertainties on salt cavern developments, and the variation in seismic response expected under different fluid saturations. The internal structure of the Zechstein Supergroup shows high levels of deformation and geometries that increase in complexity basin-ward. The internal deformation was interpreted and characterised, identifying six unique deformation styles which were parametrised and mapped spatially. This has implications for storage site suitability. Geological uncertainties were quantified for salt cavern developments, using a stochastic workflow that was developed to model potential cavern emplacement locations and hydrogen capacity. The potential hydrogen storage capacity in salt caverns in the UK sector of the Southern North Sea (80+ PWh) is far greater than any potential storage demand (100 TWh). Total energy storage demand could be met with as few as 73 caverns in an area 28 km2. The variation in the seismic response of siliciclastic reservoirs on the United Kingdom’s continental shelf was investigated after fluid substitution of non-hydrocarbon fluids to further understand seismic monitoring approaches. The results show that typical monitoring approaches, such as 4D amplitude comparisons, may not be suitable due to the limited change in elastic properties of the reservoir rocks once substituted with the pore filling fluid. This thesis quantifies and constrains the uncertainty of the subsurface for storage of non hydrocarbon fluids within the UKCS for both porous media and salt caverns. Description: PhD Thesis Wed, 01 Jan 2025 00:00:00 GMT http://theses.ncl.ac.uk/jspui/handle/10443/6743 2025-01-01T00:00:00Z http://theses.ncl.ac.uk/jspui/handle/10443/6742 Title: The development of four dimensional electrical resistivity tomography for laboratory-scale imaging of soil moisture dynamics Authors: Thaman, Narryn I J Abstract: This study considers the combination of a novel geophysical monitoring system and geotechnical point sensors for use in controlled laboratory conditions to visualise soil moisture dynamics in different engineered soils. The geophysical monitoring system, referred to here as PRIME (Proactive Infrastructure Monitoring and Evaluation system), uses electrical resistivity tomography (ERT) technology to non-invasively image subsurface moisture-driven processes. The PRIME system and point sensor arrays have been developed for near real-time data acquisition of transient soil moisture conditions in a suite of soil column experiments. This research aims to provide new tools and approaches to further our understanding of soil moisture movement to better assess shallow geotechnical assets by addressing the challenges associated with designing integrated geophysical-geotechnical laboratory-scale monitoring experiments. A total of nine soil column experiments were carried out in this research. Soil moisture content, grain size and density were changed throughout the study to gauge the proficiency of time-lapse ERT for various soils. Nine soil column experiments were conducted to evaluate the effectiveness of time-lapse ERT in various soil compositions, assessing changes in moisture content, grain size, and density. One of the main challenges associated with integrating ERT in a soil column setup is the prevalence of artefacts in the time-lapse imaging. These artefacts, presenting as high or low electrical resistivity contrasts, can be a common feature in ERT surveys and are known to reduce the accuracy of the inversion. This study takes steps to reduce the tendency of artefacts in the results by systematically identifying the source of such modelling errors and adapting the 4D ERT integrated soil column design accordingly. Alongside plotting the electrical resistivity of transient soil moisture conditions in the column experiments, petrophysical relationships derived from the ERT soil columns focus on understanding the link between soil moisture content, electrical resistivity, and suction. These relationships are crucial for improving the interpretation of time-lapse ERT data and enhancing the accuracy of soil moisture monitoring in laboratory and field applications. Findings demonstrate the potential of integrating ERT with geotechnical monitoring systems to advance understanding of soil moisture movement, with applications in geotechnical asset management and environmental engineering. Description: PhD Thesis Wed, 01 Jan 2025 00:00:00 GMT http://theses.ncl.ac.uk/jspui/handle/10443/6742 2025-01-01T00:00:00Z