Production & Supply Chain

Achieving climate neutrality goals is inseparable from the sustainable development of modern cities. Municipal wastewater treatment plants (WWTP) are among the starting points when moving cities to Net-zero Greenhouse Gas (GHG) emissions and climate neutrality. This study focuses on the analysis of the integration of green hydrogen (H2) and biomethane technologies in WWTPs and on the impact of this integration on WWTPs’ energy neutrality. This study treats WWTP as an integrated energy system with certain inputs and outputs. Currently such systems in most cases have a significantly negative energy balance and in addition fossil fuel energy sources are used. Key findings highlight that the integration of green hydrogen production in WWTPs and the efficient utilization of electrolysis by-products can make such energy systems neutral or even positive. This study provides an analysis of the main technical presumptions for the successful integration of green hydrogen and biomethane production processes in WWTP. Furthermore a case study of a real wastewater treatment plant is presented.

Offshore green hydrogen production lacks of flexible and scalable supervisory control approaches for multistack electrolyzers raising the need for extendable and high-performance solutions. This work presents a two-stage nonlinear model predictive control (MPC) method. First an MPC stage generates a discrete on-off electrolyzer switching decision through algebraic relaxation of a Boolean signal. The second MPC stage receives the stack’s on-off operation decision and optimizes hydrogen production. This is a novel approach for solving a mixed-integer nonlinear program (MINP) in multi-stack electrolyzer control applications. In order to realize the MPC the advantages of the implicit multilinear time-invariant (iMTI) model class are exploited for the first time for proton exchange membrane (PEM) electrolyzer models. A modular flexible and scalable framework in MATLAB is built. The tensor based iMTI model in canonical polyadic (CP) decomposed form breaks the curse of dimensionality and enables effective model composition for electrolyzers. Simulation results show an appropriate multilinear model representation of the nonlinear system dynamics in the operation region. A sensitivity analysis identified three numeric factors as decisive for the effectiveness of the MPC approach. The classic rule-based control methods Daisy Chain and Equal serve as reference. Over two weeks and under a wind power input profile the MPC strategy performs better regarding the objective of hydrogen production compared to the Daisy Chain (4.60 %) and Equal (0.43 %) power distribution controllers. As a side effect of the optimization a convergence of the degradation states is observed.

Since the early days of space exploration the efficient production of oxygen and hydrogen via water electrolysis has been a central task for regenerative life-support systems. Water electrolysers are however challenged by the near-absence of buoyancy in microgravity resulting in hindered gas bubble detachment from electrodes and diminished electrolysis efficiencies. Here we show that a commercial neodymium magnet enhances water electrolysis with current density improvements of up to 240% in microgravity by exploiting the magnetic polarization of the electrolyte and the magnetohydrodynamic force. We demonstrate that these interactions enhance gas bubble detachment and displacement through magnetic convection and achieve passive gas–liquid phase separation. Two model magnetoelectrolytic cells a proton-exchange membrane electrolyser and a magnetohydrodynamic drive were designed to leverage these forces and produce oxygen and hydrogen at near-terrestrial efficiencies in microgravity. Overall this work highlights achievable lightweight low-maintenance and energy-efficient phase separation and electrolyser technologies to support future human spaceflight architectures.

The Allam power cycle is a groundbreaking elevated-pressure power generation unit that utilizes oxygen and fossil fuels to generate low-cost electricity while capturing carbon dioxide (CO2) inherently. In this project we utilize the CO2 generated from the Allam cycle as feedstock for a newly envisioned industrial complex dedicated to producing renewable hydrocarbons. The industrial complex (FAAR) comprises four subsystems: (i) a Fischer–Tropsch synthesis plant (FTSP) (ii) an alkaline water electrolysis plant (AWEP) (iii) an Allam power cycle plant (APCP) and (iv) a reverse water-gas shift plant (RWGSP). Through effective material heat and power integration the FAAR complex utilizing 57.1% renewable energy for its electricity needs can poly-generate sustainable hydrocarbons (C1–C30) pure hydrogen and oxygen with near-zero emissions from natural gas and water. Economic analysis indicates strong financial performance of the development with an internal rate of return (IRR) of 18% a discounted payback period of 8.7 years and a profitability index of 2.39. The complex has been validated through rigorous modeling and simulation using Aspen Plus version 14 including sensitivity analysis.

Pilot projects to generate hydrogen using proton exchange membrane (PEM) electrolyzers coupled to nuclear power plants (NPPs) began in 2022 with further developments anticipated over the next decade. However the co-location of electrolyzers with NPPs requires an understanding and mitigation of potential risks. In this work we identify and rank failure contributors for a 1 MW PEM electrolysis system. We used fault trees to define the component failure logic parameterized them with generic data and calculated failure frequencies and minimal cut sets for four top events: hydrogen release oxygen release nitrogen release and hydrogen and oxygen mixing. We use risk reduction worth importance measures to determine the most risk-significant components. The results provide insight into primary risk drivers in PEM electrolyzer systems and provide the foundational steps towards quantitative risk assessment of large-scale PEM electrolyzers at NPPs. The results include recommended riskmitigation actions include recommendations about design maintenance and monitoring strategies.

Hydrogen energy generation faces challenges in efficiency and economic viability due to reliance on scarce noble metal catalysts. This study aimed to develop platinum-doped nickel-iron metal-organic framework (Pt-NiFe-MOF) catalysts with controlled metal ratios and pore architecture for enhanced water electrolysis. The NiFe-MOF framework was first synthesized via a solvothermal method which was then subjected to post-synthetic modification to introduce controlled platinum loadings (0.5- 2.0 wt%). The pore structure was tuned using a mixed-linker strategy (H₄DOBDC ratios 1:0 to 1:1). Catalysts were characterized using PXRD HRTEM BET XPS and ICP-OES techniques. Electrochemical performance was analyzed in 1.0 M KOH. A custom-designed integrated electrolysis system at 75 °C assessed practical performance. The Pt-NiFe-MOF-1.0 catalyst with H₄DOBDC ratio of 1:0.5 achieved remarkable effectiveness requiring overpotentials of only 253 mV for OER and 58 mV for HER when operating at 10 mA/cm². This catalyst featured an optimal pore diameter of 4.2 nm and surface area of 1325 m²/g. DFT calculations revealed platinum incorporation created synergistic effects by modifying hydrogen binding energies. Furthermore DFT calculations and XPS analysis revealed that the role of platinum in the OER is not direct catalysis but rather a powerful electronic modulation effect; Pt dopants withdraw electron density from adjacent Ni and Fe centers promoting the formation of higher-valent Ni³⁺/Fe³⁺ species that are intrinsically more active and lowering the energy barrier for the rate-determining O-O bond formation step. The integrated system achieved 1.62V at 100 mA/cm² with 75.8% energy efficiency maintaining stability for 200 h with 15–30 times lower precious metal loading than conventional systems. Strategic incorporation of low platinum concentrations within optimized NiFe-MOF structures significantly enhances water electrolysis performance while maintaining economic viability advancing development of industrial-scale hydrogen generation systems.

Electrolysis utilizing renewable electricity is an environmentally friendly non-polluting and sustainable method of hydrogen production. Seawater is the most desirable and inexpensive electrolyte for this process to achieve commercial acceptance compared to competing hydrogen production technologies. We reviewed metal–organic frameworks as possible electrocatalysts for hydrogen production by seawater electrolysis. Metal–organic frameworks are interesting for seawater electrolysis due to their large surface area tunable permeability and ease of functional processing which makes them extremely suitable for obtaining modifiable electrode structures. Here we discussed the development of metal– organic framework-based electrocatalysts as multifunctional materials with applications for alkaline PEM and direct seawater electrolysis for hydrogen production. Their advantages and disadvantages were examined in search of a pathway to a successful and sustainable technology for developing electrode materials to produce hydrogen from seawater.

Hydrogen recognized as a critical energy source requires green production methods such as proton exchange membrane water electrolysis (PEMWE) powered by renewable energy. This is a key step toward sustainable development with economic analysis playing an essential role. Life cycle costing (LCC) is commonly used to evaluate economic feasibility but traditional LCC analyses often provide a single cost outcome which limits their applicability across diverse regional contexts. To address these challenges a Python-based tool is developed in this paper integrating a bottom-up approach with net present value (NPV) calculations and Monte Carlo simulations. The tool allows users to manage uncertainty by intervening in the input data producing a range of outcomes rather than a single deterministic result thus offering greater flexibility in decision-making. Applying the tool to a 5 MW PEMWE plant in Germany the total cost of ownership (TCO) is estimated to range between €52 million and €82.5 million with hydrogen production costs between 5.5 and 11.4 €/kg H2. There is a 95% probability that actual costs fall within this range. Sensitivity analysis reveals that energy prices are the key contributors to LCC accounting for 95% of the variance in LCC while iridium membrane materials and power electronics contribute to 75% of the variation in construction-phase costs. These findings underscore the importance of renewable energy integration and circular economy strategies in reducing LCC.

Hydrogen energy is key for the global green energy transition and biomass thermochemical has become an important option for green hydrogen production due to its carbon neutrality advantage. Pyrolysis is the initial step of thermochemical technologies. A systematic analysis of the mechanism of H2 production from biomass pyrolysis is significant for the subsequent optimal design of efficient biomass thermochemical H2 production technologies. Biomass is mainly composed of cellulose hemicellulose and lignin and differences in their physicochemical properties and structures directly affect the pyrolysis hydrogen production process. In this study thermogravimetry-mass spectrometry-Fourier transform infrared spectroscopy (TG-MS-FTIR) was employed and fixed-bed pyrolysis experiments were conducted to systematically investigate the pyrolysis of biomass component with focusing on hydrogen production. According to the results of TG-MS-FTIR experiments hemicellulose produced hydrogen through the breaking of C-H bonds in short chains and acetyl groups as well as secondary cracking of volatiles and condensation of aromatic rings at high temperatures. Cellulose produced hydrogen through the breaking of C-H bonds in volatiles generated from sugar ring cleavage along with char gasification and condensation of aromatic rings at high temperatures. Lignin produced hydrogen through ether bond cleavage breaking of methoxy groups as well as cleavage of phenylpropane side chains and condensation of aromatic rings at high temperatures. Results from fixed-bed pyrolysis experiments further showed that hemicellulose exhibited the strongest hydrogen production capacity with the maximum H2 production efficiency of 6.09 mmol/g the maximum H2 selectivity of 17.79% and the maximum H2 effectiveness of 59% at 800°C.

Presently there is no single clear route for the near-term production of the huge volumes of CO2-free hydrogen necessary for the global transition to any type of hydrogen economy. All conventional routes to produce hydrogen from hydrocarbon fossil fuels (notably natural gas) involve the production—and hence the emission—of CO2 most notably in the steam methane reforming (SMR) process. Our recent studies have highlighted another route; namely the critical role played by the microwave-initiated catalytic pyrolysis decomposition or deconstruction of fossil hydrocarbon fuels to produce hydrogen with low to near-zero CO2 emissions together with high-value solid nanoscale carbonaceous materials. These innovations have been applied firstly to wax then methane crude oil diesel then biomass and most recently Saudi Arabian light crude oil as well as plastics waste. Microwave catalysis has therefore now emerged as a highly effective route for the rapid and effective production of hydrogen and high-value carbon nanomaterials co-products in many cases accompanied by low to near-zero CO2 emissions. Underpinning all of these advances has been the important concept from solid state physics of the so-called Size-Induced-Metal-Insulator Transition (SIMIT) in mesoscale or mesoscopic particles of catalysts. The mesoscale refers to a range of physical scale in-between the micro- and the macro-scale of matter (Huang W Li J and Edwards PP 2018 Mesoscience: exploring the common principle at mesoscale Natl. Sci. Rev. 5 321-326 (doi:10.1093/nsr/nwx083)). We highlight here that the actual physical size of the mesoscopic catalyst particles located close to the SIMIT is the primary cause of their enhanced microwave absorption and rapid heating of particles to initiate the catalytic—and highly selective—breaking of carbon–hydrogen bonds in fossil hydrocarbons and plastics to produce clean hydrogen and nanoscale carbonaceous materials. Importantly also since the surrounding ‘bath’ of hydrocarbons is cooler than the microwave-heated catalytic particles themselves the produced neutral hydrogen molecule can quickly diffuse from the active sites. This important feature of microwave heating thereby minimizes undesirable side reactions a common feature of conventional thermal heating in heterogeneous catalysis. The low to near-zero CO2 production of hydrogen via microwave-initiated decomposition or cracking of abundant hydrocarbon fossil fuels may be an interim viable alternative to the conventional widely-used SMR that a highly efficient process but unfortunately associated with the emission of vast quantities of CO2. Microwave-initiated catalytic decomposition also opens up the intriguing possibility of using distributed methane in the current natural gas structure to produce hydrogen and high-value solid carbon at either central or distributed sites. That approach will lessen many of the safety and environmental concerns associated with transporting hydrogen using the existing natural gas infrastructure. When completely optimized microwave-initiated catalytic decomposition of methane (and indeed all hydrocarbon sources) will produce no aerial carbon (CO2) and only solid carbon as a co-product. Furthermore reaction conditions can surely be optimized to target the production of high-quality synthetic graphite as the major carbon-product; that material of considerable importance as the anode material for lithium-ion batteries. Even without aiming for such products derived from the solid carbon co-product it is of course far easier to capture solid carbon rather than capturing gaseous CO2 at either the central or distributed sites. Through microwave-initiated catalytic pyrolysis this decarbonization of fossil fuels can now become the potent source of sustainable hydrogen and high-value carbon nanomaterials.