Multi-effect distillation: a sustainable option to large-scale green hydrogen production using solar energy

Development of sustainable, gigawatt capacity green hydrogen will require both renewable energy and water inputs, along with careful management of the waste heat produced by these processes (i.e., 9.3e16.7 kWhth=kgH2 for a 70e80% stack efficiency, high heat value). Here we compare the water demands and operating costs for a solar-driven electrolyser facility (powered by solar PV) operating on desalinated seawater produced using reverse osmosis or low-temperature multi-effect distillation. The waste heat was managed via passive cooling, evaporative cooling or through thermal recovery. It was found that the costs for low-temperature multi-effect distillation were up to 85% lower than reverse osmosis and generated 50e270L/ kgH2 of surplus water for ancillary benefit. This work challenges conventional wisdom surrounding the use of membrane desalination for meeting the water demands, offering compelling reasons for thermal desalination to be employed in large-scale production of green hydrogen

Angstrom‐confined Electrochemical Synthesis of Sub‐unit Cell non van der Waals 2D Metal Oxides

Bottom-up electrochemical synthesis of atomically thin materials is desirable yet challenging, especially for non-van der Waals (vdW) materials. Thicknesses below few nm have not been reported yet, posing the question how thin can non-vdW materials be electrochemically synthesized? This is important as materials with (sub-) unit cell thickness often show remarkably different properties compared to their bulk form or thin films of several nm thickness. Here, we introduce a straightforward electrochemical method utilizing the angstrom-confinement of laminar reduced graphene oxide (rGO) nanochannels to obtain a centimeter-scale network of atomically thin (< 4.3 Å) 2D-transition metal oxides (2D-TMO). The angstrom-confinement provides a thickness limitation, forcing sub-unit cell growth of 2D-TMO with oxygen and metal vacancies. We showcase that Cr2O3, a material without significant catalytic activity for OER in bulk form, can be activated as a high-performing catalyst if synthesized in the 2D sub-unit cell form. Our method displays the high activity of sub-unit cell form while retaining the stability of bulk form, promising to yield unexplored fundamental science and applications. We show that while retaining the advantages of bottom-up electrochemical synthesis like simplicity, high yield, and mild conditions, the thickness of TMO can be limited to sub-unit cell dimensions

Enhanced graphitic domains of unreduced graphene oxide and the interplay of hydration behaviour and catalytic activity

Previous studies indicate that the properties of graphene oxide (GO) can be significantly improved by enhancing its graphitic domain size through thermal diffusion and clustering of functional groups. Remarkably, this transition takes place below the decomposition temperature of the functional groups and thus allows fine-tuning of graphitic domains without compromising with the functionality of GO. By studying the transformation of GO under mild thermal treatment, we directly observe this size enhancement of graphitic domains from originally 40 nm2 to 200 nm2 through an extensive transmission electron microscopy (TEM) study. Additionally, we confirm the integrity of the functional groups during this process by comprehensive chemical analysis. A closer look into the process confirms the theoretically predicted relevance for the room temperature stability of GO. We further investigate the influence of enlarged graphitic domains on the hydration behaviour of GO and catalytic performance of single-atom catalysts supported by GO. Surprisingly, both, the water transport and catalytic activity are damped by the heat treatment. This allows us to reveal the critical role of water transport in laminated 2D materials as catalysts

Reduction of carbon dioxide into value added chemicals and fuel

Electrochemical CO2 reduction reaction (CO2RR) systems are a viable strategy to mitigate the rising CO2 level in the atmosphere. If powered by photovoltaic cells, these systems also shed light onto the storage as well as the distribution of the intermittent and diffusive solar energy. At present, precious metals such as Au and Pd are regarded as benchmark catalysts for CO2RR to generate CO, while their high-cost would inevitably impair the potential of large-scale implementation. In addition to generating CO, the conversion of CO2 into liquid products such as formate, ethanol and methanol are also of extensive interest as the liquid phase products can be readily stored, transported and utilized within existing infrastructure. However, current benchmarked catalysts for liquid production suffer from poor product selectivity and stability issues meanwhile requiring high applied overpotentials. The aim of this research project is to elucidate the abovementioned barriers by designing scalable catalysts for the conversion of CO2 to value added chemicals. In this regard, a range of novel CO2RR catalysts are developed using tailor-made fabrication techniques: (i) three-dimensional porous silver foam (AgFoam) to improve mass transport, (ii) defect-rich nitrogen removed mesoporous carbon catalyst (NRMC) as a metal-free alternative for CO generation, (iii) surface engineered tin foil (An-Sn) to expose more SnOx/Sn interfaces, (iv) mesoporous tin oxide (m-SnO2) with high oxygen vacancy defects, and (v) heterostructured Cu sandwich electrode that maintained the presence of Cu2+/Cu+ interfaces. The catalytic properties of the above-mentioned catalysts were then investigated with electrochemical techniques namely, cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (i-t), impedance spectroscopy (EIS), etc. and the products were detected with the aid of gas chromatograph (GC) and nuclear magnetic resonance (NMR). The physiochemical properties of the catalysts were also determined with the aid of a range of characterization techniques namely, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, Electron Paramagnetic Resonance (EPR), Brunauer-Emmet-Teller (BET) and Focused Ion Beam TEM (FIB-TEM). Density Functional Theory (DFT) calculations carried out were used to confirm the experimental findings. Overall, a clear relationship between the catalytic activity and physiochemical properties of the catalysts were demonstrated and new active sites for CO2RR were revealed

Gas Transition: Renewable Hydrogen’s Future in Eastern Australia’s Energy Networks

The energy transition for a net-zero future will require deep decarbonisation that hydrogen is uniquely positioned to facilitate. This technoeconomic study considers renewable hydrogen production, transmission and storage for energy networks using the National Electricity Market (NEM) region of Eastern Australia as a case study. Plausible growth projections are developed to meet domestic demands for gas out to 2040 based on industry commitments and scalable technology deployment. Analysis using the discounted cash flow technique is performed to determine possible levelised cost figures for key processes out to 2050. Variables include geographic limitations, growth rates and capacity factors to minimise abatement costs compared to business-as-usual natural gas forecasts. The study provides an optimistic outlook considering renewable power-to-X opportunities for blending, replacement and gas-to-power to show viable pathways for the gas transition to green hydrogen. Blending is achievable with modest (3%) green premiums this decade, and substitution for natural gas combustion in the long-term is likely to represent an abatement cost of AUD 18/tCO2-e including transmission and storage

Photocatalytic Technology for Palm Oil Mill Effluent (POME) Wastewater Treatment: Current Progress and Future Perspective

The palm oil industry produces liquid waste called POME (palm oil mill effluent). POME is stated as one of the wastes that are difficult to handle because of its large production and ineffective treatment. It will disturb the ecosystem with a high organic matter content if the waste is disposed directly into the environment. The authorities have established policies and regulations in the POME waste quality standard before being discharged into the environment. However, at this time, there are still many factories in Indonesia that have not been able to meet the standard of POME waste disposal with the existing treatment technology. Currently, the POME treatment system is still using a conventional system known as an open pond system. Although this process can reduce pollutants’ concentration, it will produce much sludge, requiring a large pond area and a long processing time. To overcome the inability of the conventional system to process POME is believed to be a challenge. Extensive effort is being invested in developing alternative technologies for the POME waste treatment to reduce POME waste safely. Several technologies have been studied, such as anaerobic processes, membrane technology, advanced oxidation processes (AOPs), membrane technology, adsorption, steam reforming, and coagulation. Among other things, an AOP, namely photocatalytic technology, has the potential to treat POME waste. This paper provides information on the feasibility of photocatalytic technology for treating POME waste. Although there are some challenges in this technology’s large-scale application, this paper proposes several strategies and directions to overcome these challenges

Antipoisoning Nickel-Carbon Electrocatalyst for Practical Electrochemical CO2 Reduction to CO

The feasibility of utilizing electrochemical reduction of CO2 (CO2RR) to close the global carbon cycle is hindered by the absence of practical electrocatalysts that can be adopted in large CO2 emitting sources with impurities. To address this, we use density functional theory (DFT) calculations to design a strategy to develop Ni coordinated graphitic carbon shells (referred as Ni@NC-900) catalyst. This strategy not only prolongs stability and endows antipoisoning properties of the catalyst but also reforms the electronic structure of the outer graphitic carbon shell to make it active for CO2RR. As a result, Ni@ NC-900 demonstrates a high conversion of CO2 to CO with a Faradaic efficiency (FECO) of 96% and a partial current density for CO (jCO) of ∼−17 mA cm−2 at an applied potential of −1 V versus reversible hydrogen electrode (RHE). This activity can be further scaled up to attain a jCO of ∼30 mA cm−2 for 18 h at a cell voltage of 2.6 V in a high-throughput continuous gas diffusion electrode (GDE) system. In addition to exhibiting high activity and stability, Ni@NC-900 displays exceptional tolerance toward impurities (from SOx, NOx, CN−), highlighting the suitability of these rationally designed catalysts for large-scale application in fossil-fuel based power plantsThe work was supported by the Australian Research Council (ARC) under the Laurate Fellowship Scheme FL-140100081, Discovery Early Career Researcher Award DE170100375 and funding from the UNSW Digital Grid Futures Institute, UNSW Sydney under a crossdisciplinary fund scheme

Designing optimal integrated electricity supply configurations for renewable hydrogen generation in Australia

Summary: The high variability and intermittency of wind and solar farms raise questions of how to operate electrolyzers reliably, economically, and sustainably using predominantly or exclusively variable renewables. To address these questions, we develop a comprehensive cost framework that extends to include factors such as performance degradation, efficiency, financing rates, and indirect costs to assess the economics of 10 MW scale alkaline and proton-exchange membrane electrolyzers to generate hydrogen. Our scenario analysis explores a range of operational configurations, considering (i) current and projected wholesale electricity market data from the Australian National Electricity Market, (ii) existing solar/wind farm generation curves, and (iii) electrolyzer capital costs/performance to determine costs of H2 production in the near (2020–2040) and long term (2030–2050). Furthermore, we analyze dedicated off-grid integrated electrolyzer plants as an alternate operating scenario, suggesting oversizing renewable nameplate capacity with respect to the electrolyzer to enhance operational capacity factors and achieving more economical electrolyzer operation