Publications

Photoelectrochemical (PEC) water splitting is a promising technology for solar hydrogen production to build a sustainable renewable and clean energy economy. Given the complexity of the PEC water splitting processes it is important to note that developing in-situ techniques for studying PEC water splitting presents a formidable challenge. This review is aimed at highlighting advantages and disadvantages of each technique while offering a pathway of potentially combining several techniques to address different aspects of interfacial processes in PEC water splitting. We reviewed recent progress in various techniques and approaches utilized to study PEC water splitting focusing on spectroscopic and scanning-probe methods.

In response to the global climate emergency governments across the world are aiming to lower greenhouse gas emissions to slow the damaging effects of climate change.<br/>The Scottish Government has set a target of net zero emissions by 2045. Already a global leader in renewable energy and low-carbon technology deployment Scotland’s energy landscape is set to undergo more change as it moves toward becoming carbon-neutral. Key to that change will be the transition from natural gas to zero-carbon gases like hydrogen and biomethane.<br/>Scotland’s north-east and central belt are home to some of its largest industrial carbon emitters. The sector’s reliance on natural gas means that it emits 11.9Mt of CO2 emissions per year says NECCUS: the equivalent of 2.6 million cars or roughly all the cars in Scotland. Most homes and businesses across Scotland also use natural gas for heating.<br/>Our North-East Network and Industrial Cluster project is laying the foundations for the rapid decarbonisation of this high-emitting sector. We’ve published a report outlining the practical steps needed to rapidly decarbonise a significant part of Scotland’s homes and industry. It demonstrates how hydrogen can play a leading role in delivering the Scottish Government’s target of one million homes with low carbon heat by 2030.<br/>The research published with global consulting and engineering advisor Wood sets out a transformational and accelerated pathway to 100% hydrogen for Scotland’s gas networks which you can see on the map below. It also details the feasibility of a CO2 collection network to securely capture transport and store carbon dioxide emissions deep underground.

This paper aims to review existing energy-sector and hydrogen-energy-related legal policy and strategy documents in the ECOWAS region. To achieve this aim current renewable-energyrelated laws acts of parliament executive orders presidential decrees administrative orders and memoranda were analyzed. The study shows that ECOWAS countries have strived to design consistent legal instruments regarding renewable energy in developing comprehensive legislation and bylaws to consolidate it and to encourage investments in renewable energy. Despite all these countries having a legislative basis for regulating renewable energy there are still weaknesses that revolve around the law and policy regarding its possible application in green hydrogen production and use. The central conclusion of this review paper is that ECOWAS member states presently have no official hydrogen policies nor bylaws in place. The hydrogen rise presents a challenge and opportunity for members to play an important role in the fast-growing global hydrogen market. Therefore these countries need to reform their regulatory frameworks and align their policies by introducing green hydrogen production in order to accomplish their green economy transition for the future and to boost the continent’s sustainable development.

The European Union is aiming at reaching greenhouse gas (GHG) emission neutrality in 2050. Austria’s current greenhouse gas emissions are 80 million t/year. Renewable Energy (REN) contributes 32% to Austria’s total energy consumption. To decarbonize energy consumption a substantial increase in energy generation from renewable energy is required. This increase will add to the seasonality of energy supply and amplifies the seasonality in energy demand. In this paper the seasonality of energy supply and demand in a Net-Zero Scenario are analyzed for Austria and requirements for hydrogen storage derived. We looked into the potential usage of hydrogen in Austria and the economics of hydrogen generation and technology and market developments to assess the Levelized Cost of Hydrogen (LCOH). Then we cover the energy consumption in Austria followed by the REN potential. The results show that incremental potential of up to 140 TWh for hydropower photovoltaic (PV) and wind exists in Austria. Hydropower generation and PV is higher in summer- than in wintertime while wind energy leads to higher energy generation in wintertime. The largest incremental potential is PV with agrivoltaic systems significantly increasing the area amenable for PV compared with PV usage only. Battery Electric Vehicles (BEV) and Fuel Cell Vehicles (FCV) use energy more efficiently than Internal Combustion Engine (ICE) cars; however the use of hydrogen for electricity generation significantly decreases the efficiency due to electricity–hydrogen– electricity conversion. The increase in REN use and the higher demand for energy in Austria in wintertime require seasonal storage of energy. We developed three scenarios Externally Dependent Scenario (EDS) Balanced Energy Scenario (BES) or Self-Sustained Scenario (SSS) for Austria. The EDS scenario assumes significant REN import to Austria whereas the SSS scenario relies on REN generation within Austria. The required hydrogen storage would be 10.82 bn m3 for EDS 13.34 bn m3 for BES and 18.69 bn m3 for SSS. Gas and oil production in Austria and the presence of aquifers indicates that sufficient storage capacity might be available. Significant technology development is required to be able to implement hydrogen as an energy carrier and to balance seasonal energy demand and supply.

A thermochemical recuperation (TCR) reactor was developed and experimentally evaluated with the objective to improve dual-fuel diesel–ammonia compression ignition engines. The novel system simultaneously decomposed ammonia into a hydrogen-containing mixture to allow high diesel fuel replacement ratios and oxidized unburned ammonia emissions in the exhaust overcoming two key shortcomings of ammonia combustion in engines from the previous literature. In the experimental work a multi-cylinder compression ignition engine was operated in dual-fuel mode using intake-fumigated ammonia and hydrogen mixtures as the secondary fuel. A full-scale catalytic TCR reactor was constructed and generated the fuel used in the engine experiments. The results show that up to 55% of the total fuel energy was provided by ammonia on a lower heating value basis. Overall engine brake thermal efficiency increased for modes with a high exhaust temperature where ammonia decomposition conversion in the TCR reactor was high but decreased for all other modes due to poor combustion efficiency. Hydrocarbon and soot emissions were shown to increase with the replacement ratio for all modes due to lower combustion temperatures and in-cylinder oxidation processes in the late part of heat release. Engine-out oxides of nitrogen (NOx) emissions decreased with increasing diesel replacement levels for all engine modes. A higher concentration of unburned ammonia was measured in the exhaust with increasing replacement ratios. This unburned ammonia predominantly oxidized to NOx species over the oxidation catalyst used within the TCR reactor. Ammonia substitution thus increased post-TCR reactor ammonia and NOx emissions in this work. The results show however that engine-out NH3 -to-NOx ratios were suitable for passive selective catalytic reduction thus demonstrating that both ammonia and NOx from the engine could be readily converted to N2 if the appropriate catalyst were used in the TCR reactor.

The target of net-zero emissions set by the 2015 Paris Agreement has strongly commissioned the energy production sector to promote decarbonization renewable sources exploitation and systems efficiency. In this framework the utilization of hydrogen as a long-term energy carrier has great potential. This paper is concerned with the combustion characterization in a non-premixed gas turbine burner originally designed for natural gas when it is fed with NG-H2 blends featuring hydrogen content from 0 to 50% in volume. The final aim is to retrofit a 40 MW gas turbine. Starting from the operational data of the engine a CFD model of the steady-state combustion process has been developed with reference to the base load NG conditions by reducing the fuel mass-flow rate by up to 17% to target the baseline turbine inlet temperature. When the fuel is blended with hydrogen for a given temperature at turbine inlet an increase in the peak temperature up to 800 K is obtained if no countermeasures are taken. Furthermore the flame results are more intense and closer to the injector in the case of hydrogen blending. The results of this work hint at the necessity of carefully analyzing the possible NOx compensation strategies as well as the increased thermal stresses on the injector.

The simultaneous photocatalytic H2 evolution with environmental remediation over semiconducting metal oxides is a fascinating process for sustainable fuel production. However most of the previously reported photocatalytic reforming showed nonstoichiometric amounts of the evolved H2 when organic substrates were used. To explain the reasons for this phenomenon a careful analysis of the products and intermediates in gas and aqueous phases upon the photocatalytic hydrogen evolution from oxalic acid using Pt/TiO2 was performed. A quadrupole mass spectrometer (QMS) was used for the continuous flow monitoring of the evolved gases while high performance ion chromatography (HPIC) isotopic labeling and electron paramagnetic resonance (EPR) were employed to understand the reactions in the solution. The entire consumption of oxalic acid led to a ~30% lower H2 amount than theoretically expected. Due to the contribution of the photoKolbe reaction mechanism a tiny amount of formic acid was produced then disappeared shortly after the complete consumption of oxalic acid. Nevertheless a much lower concentration of formic acid was generated compared to the nonstoichiometric difference between the formed H2 and the consumed oxalic acid. Isotopic labeling measurements showed that the evolved H2 HD and/or D2 matched those of the solvent; however using D2O decreased the reaction rate. Interestingly the presence of KI as an additional hole scavenger with oxalic acid had a considerable impact on the reaction mechanism and thus the hydrogen yield as indicated by the QMS and the EPR measurements. The added KI promoted H2 evolution to reach the theoretically predictable amount and inhibited the formation of intermediates without affecting the oxalic acid degradation rate. The proposed mechanism by which KI boosts the photocatalytic performance is of great importance in enhancing the overall energy efficiency for hydrogen production via photocatalytic organic reforming.

The European Community requires a vehicle-level bonfire test for vehicles using plastic fuel tanks for conventional fuels (ECE R-34 Annex 5). A similar test could be applied to hydrogen-fuelled vehicles. It would test a realistic vehicle with its complete fuel and safety systems. An advantage of such a test is that the same test could be applied independent of the hydrogen storage technology (compressed gas liquid or hydride). There are currently standards for bonfire testing of a bare Compressed Natural Gas (CNG) tank and its Pressure Relief Device (PRD). This standard is FMVSS 304 in the U.S. and ISO 15869-1 in Europe. Japan has a similar standard. It requires that a bare tank and its associated PRD be subjected to a propane flame for 20 minutes. The tank must either survive or safely vent its contents. No modern composite wound tank is expected to survive for 20 minutes – so this is not a tank test but really a PRD test. The test procedure requires the PRD to be shielded from direct impingement of the flames – but the shield is not well specified. If it shields the PRD too well the PRD will not activate and the tank will burst. This paper describes the results of a CNG and a hydrogen tank burst from such tests. The mechanical energy released is enormous. It is simply unacceptable to allow the tank to burst – the PRD and venting system must work. Organizations in the U.S Europe and Japan are in the process of modifying the CNG tank bonfire test for compressed hydrogen storage. A bare tank with a single PRD is not a good simulation of a hydrogen fuel system installed in an actual vehicle. There will usually be multiple tanks plumbed together at either the tank pressure or at the intermediate pressure (after the pressure regulator). There may be more than one PRD. The tank may be shielded (from debris) or insulated to protect it from an underbody pool fire. Also the heat transfer from the simulated pool fire (propane flame) will be very different when mounted in a vehicle versus the bare tank test. A vehicle-level pool fire test will alleviate these problems. It is therefore recommended that the bare tank test be replaced by or augmented with a vehicle-level bonfire test similar to ECE R-34 Annex 5.

The rapid conversion of conventional powertrain technologies to climate-neutral new energy vehicles requires the ramping of electrification. The popularity of fuel cell electric vehicles with improved fuel economy has raised great attention for many years. Their use of green hydrogen is proposed to be a promising clean way to fill the energy gap and maintain a zero-emission ecosystem. Their complex architecture is influenced by complex multiphysics interactions driving patterns and environmental conditions that put a multitude of power requirements and boundary conditions around the vehicle subsystems including the fuel cell system the electric motor battery and the vehicle itself. Understanding its optimal fuel economy requires a systematic assessment of these interactions. Artificial intelligence-based machine learning methods have been emerging technologies showing great potential for accelerated data analysis and aid in a thorough understanding of complex systems. The present study investigates the fuel economy peaks during an NEDC in fuel cell electric vehicles. An innovative approach combining traditional multiphysics analyses design of experiments and machine learning is an effective blend for accelerated data supply and analysis that accurately predicts the fuel consumption peaks in fuel cell electric vehicles. The trained and validated models show very accurate results with less than 1% error.

This work focuses on the experimental and numerical investigation of maximum overpressure and pressure dynamics during ignited hydrogen releases in a storage enclosure e.g. in marine vessel or rail carriage with limited vent size area i.e. the pressure peaking phenomenon (PPP) revealed theoretically at Ulster University in 2010. The CFD model previously validated against small scale experiments in a 1 m3 enclosure is employed here to simulate real-scale tests performed by the University of South-Eastern Norway (USN) in a chamber with a volume of 15 m3 . The numerical study compares two approaches on how to model the ignited hydrogen release conditions for under-expanded jets: (1) notional nozzle concept model with inflow boundary condition and (2) volumetric source model in the governing conservation equations. For the test with storage pressure of 11.78 MPa both approaches reproduce the experimental pressure dynamics and the pressure peak with a maximum 3% deviation. However the volumetric source approach reduces significantly the computational time by approximately 3 times (CFL = 0.75). The sensitivity analysis is performed to study the effect of CFL number the size of the volumetric source and number of iterations per time step. An approach based on the use of a larger size volumetric source and uniform coarser grid with a mesh size of a vent of square size is demonstrated to reduce the duration of simulations by a factor of 7.5 compared to the approach with inflow boundary at the notional nozzle exit. The volumetric source model demonstrates good engineering accuracy in predicting experimental pressure peaks with deviation from −14% to +11% for various release and ventilation scenarios as well as different volumetric source sizes. After validation against experiments the CFD model is employed to investigate the effect of cryogenic temperature in the storage on the overpressure dynamics in the enclosure. For a storage pressure equal to 11.78 MPa it is found that a decrease of storage temperature from 277 K to 100 K causes a twice larger pressure peak in the enclosure due to the pressure peaking phenomenon.