Transmission, Distribution & Storage

A CsH and KH co-doped Mg(NH₂)₂/2LiH composite was prepared with a composition of Mg(NH₂)₂/2LiH–(0.08 − x)CsH–xKH and the hydrogen storage characteristics was systematically investigated. The results showed that the presence of KH further improved the reaction thermodynamics and kinetics of hydrogen storage in a CsH-containing Mg(NH₂)₂/2LiH system. A sample with 0.04 mol CsH and 0.04 mol KH had optimal hydrogen storage performance; its dehydrogenation could proceed at 130 °C and hydrogenation at 120 °C with 4.89 wt% of hydrogen storage capacity. At 130 °C a 25-fold increase in the dehydrogenation rate was achieved for the CsH and KH co-doped sample. More importantly the CsH and KH co-doped sample also had good cycling stability because more than 97% of the hydrogen storage capacity (4.34 wt%) remained for theMg(NH₂)₂/2LiH–0.04CsH–0.04KH sample after 30 cycles. A structural characterization revealed that added CsH and KH participated in the dehydrogenation and hydrogenation reactions by reversibly forming mixed amides of Li–K and Cs–Mg which caused the improved hydrogen storage thermodynamics and kinetics.

This paper has experimentally proved that hydrogen accumulates in large quantities in metal-ceramic and pocket electrodes of alkaline batteries during their operation. Hydrogen accumulates in the electrodes in an atomic form. After the release of hydrogen from the electrodes a powerful exothermic reaction of atomic hydrogen recombination with a large energy release occurs. This exothermic reaction is the cause of thermal runaway in alkaline batteries. For the KSL-15 battery the gravimetric capacity of sintered nickel matrix of the oxide-nickel electrode as hydrogen storage is 20.2 wt% and cadmium electrode is 11.5 wt%. The stored energy density in the metal-ceramic matrix of the oxide-nickel electrode of the battery KSL-15 is 44 kJ/g and in the cadmium electrode it is 25 kJ/g. The similar values for the KPL-14 battery are as follows. The gravimetric capacity of the active substance of the pocket oxide-nickel electrode as a hydrogen storage is 22 wt% and the cadmium electrode is 16.9 wt%. The density of the stored energy in the active substance oxide-nickel electrode is 48 kJ/g and in the active substance of the cadmium electrode it is 36.8 kJ/g. The obtained results of the accumulation of hydrogen energy in the electrodes by the electrochemical method are three times higher than any previously obtained results using the traditional thermochemical method.

Hydrogen gas pressure is an important test parameter when considering materials for high-pressure hydrogen applications. A large set of data on the effect of hydrogen gas pressure on mechanical properties in gaseous hydrogen experiments was reviewed. The data were analyzed by converting pressures into fugacities (f) and by fitting the data using an f|n| power law. For 95% of the data sets |n| was smaller than 0.37 which was discussed in the context of (i) rate-limiting steps in the hydrogen reaction chain and (ii) statistical aspects. This analysis might contribute to defining the appropriate test fugacities (pressures) to qualify materials for gaseous hydrogen applications.

The integration and control of energy systems for power generation consists of multiple heterogeneous subsystems such as chemical electrochemical and thermal and contains challenges that arise from the multi-way interactions due to complex dynamic responses among the involved subsystems. The main motivation of this work is to design the control system for an autonomous automated and sustainable system that meets a certain power demand profile. A systematic methodology for the integration and control of a hybrid system that converts liquefied petroleum gas (LPG) to hydrogen which is subsequently used to generate electrical power in a high-temperature fuel cell that charges a Li-Ion battery unit is presented. An advanced nonlinear model predictive control (NMPC) framework is implemented to achieve this goal. The operational objective is the satisfaction of power demand while maintaining operation within a safe region and ensuring thermal and chemical balance. The proposed NMPC framework based on experimentally validated models is evaluated through simulation for realistic operation scenarios that involve static and dynamic variations of the power load.

Expectations for energy storage are high but large-scale underground hydrogen storage in porous media (UHSP) remains largely untested. This article identifies and discusses the scientific challenges of hydrogen storage in porous media for safe and efficient large-scale energy storage to enable a global hydrogen economy. To facilitate hydrogen supply on the scales required for a zero-carbon future it must be stored in porous geological formations such as saline aquifers and depleted hydrocarbon reservoirs. Large-scale UHSP offers the much-needed capacity to balance inter-seasonal discrepancies between demand and supply decouple energy generation from demand and decarbonise heating and transport supporting decarbonisation of the entire energy system. Despite the vast opportunity provided by UHSP the maturity is considered low and as such UHSP is associated with several uncertainties and challenges. Here the safety and economic impacts triggered by poorly understood key processes are identified such as the formation of corrosive hydrogen sulfide gas hydrogen loss due to the activity of microbes or permeability changes due to geochemical interactions impacting on the predictability of hydrogen flow through porous media. The wide range of scientific challenges facing UHSP are outlined to improve procedures and workflows for the hydrogen storage cycle from site selection to storage site operation. Multidisciplinary research including reservoir engineering chemistry geology and microbiology more complex than required for CH₄ or CO₂ storage is required in order to implement the safe efficient and much needed large-scale commercial deployment of UHSP.

Energy storage is a promising approach to address the challenge of intermittent generation from renewables on the electric grid. In this work we evaluate energy storage with a regenerative hydrogen fuel cell (RHFC) using net energy analysis. We examine the most widely installed RHFC configuration containing an alkaline water electrolyzer and a PEM fuel cell. To compare RHFC's to other storage technologies we use two energy return ratios: the electrical energy stored on invested (ESOI_e) ratio (the ratio of electrical energy returned by the device over its lifetime to the electrical-equivalent energy required to build the device) and the overall energy efficiency (the ratio of electrical energy returned by the device over its lifetime to total lifetime electrical-equivalent energy input into the system). In our reference scenario the RHFC system has an ESOI_eratio of 59 more favorable than the best battery technology available today (Li-ion ESOI_e= 35). (In the reference scenario RHFC the alkaline electrolyzer is 70% efficient and has a stack lifetime of 100 000 h; the PEM fuel cell is 47% efficient and has a stack lifetime of 10 000 h; and the round-trip efficiency is 30%.) The ESOIe ratio of storage in hydrogen exceeds that of batteries because of the low energy cost of the materials required to store compressed hydrogen and the high energy cost of the materials required to store electric charge in a battery. However the low round-trip efficiency of a RHFC energy storage system results in very high energy costs during operation and a much lower overall energy efficiency than lithium ion batteries (0.30 for RHFC vs. 0.83 for lithium ion batteries). RHFC's represent an attractive investment of manufacturing energy to provide storage. On the other hand their round-trip efficiency must improve dramatically before they can offer the same overall energy efficiency as batteries which have round-trip efficiencies of 75–90%. One application of energy storage that illustrates the trade-off between these different aspects of energy performance is capturing overgeneration (spilled power) for later use during times of peak output from renewables. We quantify the relative energetic benefit of adding different types of energy storage to a renewable generating facility using [EROI]grid. Even with 30% round-trip efficiency RHFC storage achieves the same [EROI]grid as batteries when storing overgeneration from wind turbines because its high ESOI_eratio and the high EROI of wind generation offset the low round-trip efficiency.

Nanostructured Fe₇S₈ was successfully synthesized and its catalytic effect on hydrogen absorption/desorption performance of MgH₂2 is systemically discussed. The MgH₂ + 16.7 wt% Fe7S8 composite prepared by ball-milling method offers a striking catalytic activity for hydrogenation kinetics and also reduces the initial decomposition temperature for MgH₂2. The composite of MgH₂–Fe₇S₈ can absorb 4.000 wt% of hydrogen within 1800 s at 473 K which is about twice that of pristine MgH₂ (1.847 wt%) under the same conditions. The onset hydrogen release temperature of Fe₇S₈-modified MgH₂ is 420 K which is 290 K lower than that of additive-free MgH₂ (710 K). Meanwhile the doped sample could release 4.403 wt% of hydrogen within 1800 s at 623 K as compared to 2.479 wt% of hydrogen by MgH₂. The activation energy for MgH2–Fe7S8 is about 130.0 kJ mol−1 approximately 36 kJ mol−1 lower than that of MgH₂. The hydriding process of MgH2 + 16.7 wt% Fe₇S₈ follows the nucleation and growth mechanism. The prominent hydrogen storage performances are related to the reactions between MgH₂ and Fe₇S₈. The newly formed MgS and Fe in the ball-milling process present a co-catalytic effect on the hydrogen storage performance of MgH₂2.

As a promising hydrogen storage medium methanol has many advantages such as a high hydrogen content (12.5 wt%) and low-cost. However conventional methanol–water reforming methods usually require a high temperature (>200 °C). In this research we successfully designed an effective strategy to fully convert methanol to hydrogen for at least 1900 min (∼32 h) at near-room temperature. The strategy involves two main procedures which are CH₃OH →HCOOH → H₂ and CH₃OH → NADH → H₂. HCOOH and the reduced form of nicotinamide adenine dinucleotide (NADH) are simultaneously produced through the dehydrogenation of methanol by the cooperation of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). Subsequently HCOOH is converted to H₂ by a new iridium polymer complex catalyst and an enzyme mimic is used to convert NADH to H₂ and nicotinamide adenine dinucleotide (NAD+). NAD+ can then be reconverted to NADH by repeating the dehydrogenation of methanol. This strategy and the catalysts invented in this research can also be applied to hydrogen production from other small organic molecules (e.g. ethanol) or biomass (e.g. glucose) and thus will have a high impact on hydrogen storage and applications.

The storage of hydrogen gas in underground lined rock caverns (LRCs) enables the implementation of the first fossil-free steelmaking process to meet the large demand for crude steel. Predicting the response of rock mass is important to ensure that gas leakage due to rupture of the steel lining does not occur. Analytical and numerical models can be used to estimate the rock mass response to high internal pressure; however the fitness of these models under different in situ stress conditions and cavern shapes has not been studied. In this paper the suitability of analytical and numerical models to estimate the maximum cavern wall tangential strain under high internal pressure is studied. The analytical model is derived in detail and finite element (FE) models considering both two-dimensional (2D) and three-dimensional (3D) geometries are presented. These models are verified with field measurements from the LRC in Skallen southwestern Sweden. The analytical model is inexpensive to implement and gives good results for isotropic in situ stress conditions and large cavern heights. For the case of anisotropic horizontal in situ stresses as the conditions in Skallen the 3D FE model is the best approach

The effect of different cathodic potentials applied to the X70 pipeline steel immersed in acidified and aerated synthetic soil solution under stress using a slow strain rate test (SSRT) and electrochemical impedance spectroscopy (EIS) was studied. According to SSRT results and the fracture surface analysis by scanning electron microscopy (SEM) the steel susceptibility to stress corrosion cracking (SCC) increased as the cathodic polarization increased (Ecp). This behavior is attributed to the anodic dissolution at the tip of the crack and the increment of the cathodic reaction (hydrogen evolution) producing hydrogen embrittlement. Nevertheless when the Ecp was subjected to the maximum cathodic potential applied (−970 mV) the susceptibility decreased; this behavior is attributed to the fact that the anodic dissolution was suppressed and the process of the SCC was dominated only by hydrogen embrittlement (HE). The EIS results showed that the cathodic process was influenced by the mass transport (hydrogen diffusion) due to the steel undergoing so many changes in the metallic surface as a result of the applied strain that it generated active sites at the surface.