A Survey of Green Mobile Networks: Opportunities and Challenges

The explosive development of Information and Communication Technology (ICT) has significantly enlarged both the energy demands and the CO ₂ emissions, and consequently contributes to make the energy crisis and global warming problems worse. However, as the main force of the ICT field, the mobile networks, are currently focusing on the capacity, variety and stability of the communication services, without paying too much severe concerns on the energy efficiency. The escalating energy costs and environmental concerns have already created an urgent need for more energy-efficient “green” wireless communications. In this paper, we survey and discuss various remarkable techniques toward green mobile networks to date, mainly targeting mobile cellular networks. We also summarize the current research projects related to green mobile networks, along with the taxonomy of energy-efficiency metrics. We finally discuss and elaborate future research opportunities and design challenges for green mobile networks.     

Does information and communication technology and financial development lead to environmental sustainability in India? An empirical insight

This paper examines the relationship between CO₂ emissions, electricity consumption, financial development, Economic growth, Informational Communication Technology (ICT) from 1990 to 2018 in India. We have applied the structural break co-integration approach like Gregory Hansen approach to check long-term relations between the variables. ARDL bounds testing approach is used to know the long run and short-run elasticity. We find that electricity consumption is positively contributing CO₂ emissions or reducing environmental sustainability in India. However, ICT has negative and significantly improving environmental sustainability or reducing emissions when measured in both ICT internet connection (ICT_INT) and ICT mobile Phones (ICT_MOB). Similarly, financial development and CO₂ emissions are negatively related. The result indicates the existence of Environmental Kuznets Curve in India's case. Overall, environmental sustainability achieved in ICT and financial development sectors. Therefore govt. needs to focus more on the stringent policy in electricity production by investing more in the renewable energy sector to curb environmental degradation.     

ICT and environmental sustainability: A global perspective

The positive and negative environmental impacts of information and communication technologies (ICTs) are widely debated. In theory, ICT is among the sources contributing to the increasing levels of CO₂ emissions in terms of production of ICT machinery and devices, energy consumption, and recycling of electronic waste. However, ICT is also expected to reduce CO₂ emissions on a global scale by developing smarter cities, transportation systems, electrical grids, industrial processes, and energy saving gains. These two effects work in opposite direction, creating an inverted-U relationship between ICT and CO₂ emissions. The aim of this study is to investigate this non-linear relationship between ICT and CO₂ emissions on a global scale. Given that global warming is a global issue, it is necessary to look at this relationship in countries at all levels of development. To this end, we use a panel data set consisting of 142 economies, split into 116 developing and 26 developed countries, over the period 1995–2010. The results of our empirical study confirm that the relationship between ICT and CO₂ emissions is an inverted U-shaped relationship. Moreover, while for the sample of developing countries, the ICT turning point is well above the mean value, the opposite is true for the sample of developed countries. This implies that many developed countries have already attained the level of ICT development, at which CO₂ emissions decreases as the level of ICT development improves further.     

A comparative study on cost and life‐cycle analysis for 100 MW very large‐scale PV (VLS‐PV) systems in deserts using m‐Si,a‐Si,CdTe, and CIS modules

This paper is a study of comparisons between five types of 100 MW Very Large‐Scale Photovoltaic Power Generation (VLS‐PV) Systems, from economic and environmental viewpoints. The authors designed VLS‐PV systems using typical PV modules of multi‐crystalline silicon (12·8% efficiency), high efficiency multi‐crystalline silicon (15·8%), amorphous silicon (6·9%), cadmium tellurium (9·0%), and copper indium selenium (11·0%), and evaluated them by Life‐Cycle Analysis (LCA). Cost, energy requirement, and CO₂ emissions were calculated. In addition, the authors evaluated generation cost, energy payback time (EPT), and CO₂ emission rates. As a result, it was found that the EPT is 1·5–2·5 years and the CO₂ emission rate is 9–16 g‐C/kWh. The generation cost was 11–12 US Cent/kWh on using 2 USD/W PV modules, and 19–20 US Cent/kWh on using 4 USD/W PV module price. Copyright © 2007 John Wiley & Sons, Ltd.     

Molecular Modulation of Sequestered Copper Sites for Efficient Electroreduction of Carbon Dioxide to Methane

The sustainable production of methane (CH₄) via the electrochemical conversion of carbon dioxide (CO₂) is an appealing approach to simultaneously mitigating carbon emissions and achieving energy storage in chemical bonds. Copper (Cu) is a unique material to produce hydrocarbons and oxygenates. However, selective methane generation on Cu remains a great challenge due to the preferential *CO dimerization pathway toward multi-carbon (C₂₊) products at neighboring catalytic sites. Herein, a conjugated copper phthalocyanine polymer (CuPPc) is designed by a facile solid-state method for highly selective CO₂-to-CH₄ conversion. The spatially isolated Cu N₄ sites in CuPPc favor the *CO protonation to generate the key *CHO intermediate, thus significantly promoting the formation of CH₄. As a result, the CuPPc catalyst exhibits a high CH₄ Faradaic efficiency of 55% and a partial current density of 18 mA cm⁻² at −1.25 V versus the reversible hydrogen electrode. It also stably operates for 12 h. This study may offer a new solution to regulating the chemical environment of the active sites for the development of highly efficient copper-based catalysts for electrochemical CO₂ reduction.     

Renewable energy-aware grooming in optical networks

The optical layer of a network is the energy-efficient technology to provision high bandwidths for data transport. Unfortunately, occasional electronic processing is unavoidable in current networks. This process is much more energy-consuming than the optical transport. Recent research has already yielded great improvements in terms of energy efficiency. It is, however, observed that increased energy efficiency typically leads to higher overall energy consumption. Therefore, it is imperative to reduce the environmental impact by additional means: maximizing the use of renewable energy. We present an approach to greenhouse gas (GHG) emission-reducing grooming by considering the heterogeneous distribution of fossil and renewable energy sources. We analyze various two-step solutions for the route calculation and lightpath provisioning problem in IP-over-WDM mesh networks. We show that it is possible to reduce GHG emissions at a stable level of energy consumption and improved blocking performance compared to previous energy-efficient solutions.     

Nanoconfined Molecular Catalysts in Integrated Gas Diffusion Electrodes for High-Current-Density CO2 Electroreduction

Molecular catalysts are promising catalysts to electrochemically convert CO₂ into CO with high selectivity. However, achieving industrial-level current density remains challenging due to the limitation of charge- and mass-transport in gas diffusion electrode. Herein, a novel gas diffusion electrode architecture by confining highly dispersed cobalt(II) phthalocyanine (CoPc) molecules into -graphene oxide (GO) nanosheets (denoted as CoPc@GO) is designed. Benefiting from the accelerated CO₂ diffusion and charge transport in the nanoconfined structure, the designed electrode achieves a high CO partial current density of 481.65 ± 12.50 mA cm⁻² and a cathode energy efficiency over 64% for CO. The experimentally measured CO₂ transport dynamics and molecular dynamics simulation confirm the accelerated CO₂ diffusion, while theoretical calculations reveal the decreased energy barrier of the CO₂ activation in the confined space. This study paves a new way for electrode architecture design that would accelerate the implementation of CO₂ electrolysis technology.     

An analysis of energy consumption and carbon footprints of cryptocurrencies and possible solutions

There is an urgent need to control global warming caused by humans to achieve a sustainable future. CO₂ levels are rising steadily, and while countries worldwide are actively moving toward the sustainability goals proposed during the Paris Agreement in 2015, we are still a long way to go from achieving a sustainable mode of global operation. The increased popularity of cryptocurrencies since the introduction of Bitcoin in 2009 has been accompanied by an increasing trend in greenhouse gas emissions and high electrical energy consumption. Popular energy tracking studies (e.g., Digiconomist and the Cambridge Bitcoin Energy Consumption Index (CBECI)) have estimated energy consumption ranges from 29.96 ?TWh to 135.12 ?TWh and 26.41 ?TWh to 176.98 ?TWh, respectively for Bitcoin as of July 2021, which are equivalent to the energy consumption of countries such as Sweden and Thailand. The latest estimate by Digiconomist on carbon footprints shows a 64.18 MtCO₂ emission by Bitcoin as of July 2021, close to the emissions by Greece and Oman. This review compiles estimates made by various studies from 2018 to 2021. We compare the energy consumption and carbon footprints of these cryptocurrencies with countries around the world and centralized transaction methods such as Visa. We identify the problems associated with cryptocurrencies and propose solutions that can help reduce their energy consumption and carbon footprints. Finally, we present case studies on cryptocurrency networks, namely, Ethereum 2.0 and Pi Network, with a discussion on how they can solve some of the challenges we have identified.     

Graphdiyne: A New Photocatalytic CO2 Reduction Cocatalyst

Exploring new and efficient cocatalysts to boost photocatalytic CO₂ reduction is of critical importance for solar‐to‐fuel conversion. As an emerging carbon allotrope, graphdiyne (GDY) features 2D characteristics and unique carbon–carbon bonds. Herein, a novel GDY cocatalyst coupled TiO₂ nanofibers for boosted photocatalytic CO₂ reduction, synthesized by an electrostatic self‐assembly approach is reported. First‐principle calculation and in situ X‐ray photoelectron spectroscopy measurement reveal that the delocalized electrons in GDY can hybrid with the empty orbitals in TiO₂ within the TiO₂/GDY network, leading to the formation of an internal electric field at the interfaces, pointing from GDY to TiO₂. The theoretical simulation further implies strong chemisorption and deformation of CO₂ molecules upon GDY, which can be verified by in situ diffuse reflectance infrared Fourier transform spectroscopy. These effects, in combination with the photothermal effect of GDY, result in enhanced charge separation and directed electron transfer, enhanced CO₂ adsorption and activation as well as accelerated catalytic reactions over the TiO₂/GDY heterostructure, thereby resulting in significantly improved CO₂ photoreduction efficiency and meanwhile with remarkable selectivity. This work demonstrates that GYD can function as a highly effective cocatalyst for solar energy harvesting and may be used in other catalysis processes.     

Metal–CO2 Batteries at the Crossroad to Practical Energy Storage and CO2 Recycle

Metal–CO₂ batteries show great promise in meeting the growing energy, chemical, and environmental demands of daily life and industry, because of their advantages of high flexibility and efficiency in both energy storage and CO₂ recycle applications. It has been a trend that Li/Na‐CO₂ and Zn/Al‐CO₂ systems show different developments to achieve practical energy storage (e.g., high electricity supply) and CO₂ recycling (e.g., flexible chemical production), respectively, which is often neglected. This inhibits the application of metal–CO₂ batteries in maximizing energy supply and value‐added CO₂ conversion. This progress report presents a critically selected overview of the individual developments of metal–CO₂ batteries with emphasis on diverse fundamental origins, performance advantages, and the future of these two systems. Furthermore, the reaction pathways, particularly for catalytic materials, for the Li/Na‐CO₂ and Zn/Al‐CO₂ systems are discussed. Finally, the challenges of these two systems along with a hybrid Li/Na‐CO₂ battery design that may simultaneously provide high operating voltages and flexible chemicals are outlined.     

光泵CF4 16微米激光器

本文介绍了由 TEA CO_2激光器的9R(12)跃迁线泵浦冷却的 CF_4分子,获得 16μm激光输出。泵浦光用限孔光阑得到TEMoo单横模,由低气压CO_2增益池压缩线宽,并与光泵腔良好的模式匹配下,以700mJ的泵浦源能量获得25mJ左右的16μm激光输出能量。光量子转换效率达7％左右。激光脉宽窄于150ns,该器件可在约0.5Hz重复率下,以20mJ的输出能量运转数千次。     

Covalent Organic Framework Hosting Metalloporphyrin‐Based Carbon Dots for Visible‐Light‐Driven Selective CO2 Reduction

The visible‐light‐driven photocatalytic CO₂ reduction is one appealing approach to simultaneously mitigate the energy crisis and environmental issues. It is highly desirable but challenging to selectively and efficiently convert CO₂ into desirable products. Herein, a covalent organic framework hosting metalloporphyrin‐based carbon dots (M‐PCD@TD‐COF, M = Ni, Co, and Fe) is first presented, which serves as heterogeneous catalysts for CO₂ photoreduction. M‐PCD@TD‐COF not only enriches available COF‐based catalytic materials, but also provides suitable environment for CO₂ adsorption and activation on metalloporphyrin‐based carbon dots. The advantages of the host environment in COFs are highlighted by the satisfactory catalytic activity and remarkable selectivity of CO₂‐to‐CO conversion over H₂ generation up to 98%. The photocatalytic system is effective for both pure CO₂ and the simulated flue gas. This work provides new protocols for the rational design of COF‐based heterogeneous catalysts for selective CO₂ photoreduction.     

A green trust‐distortion resistant trust management scheme on mobile ad hoc networks

Trust management is an emerging security approach used to conduct nodes' relationships in mobile ad hoc networks. It relates to assigning a trust level to each network component based on its cooperative behavior with respect to system goals. Because of its infrastructure‐less nature, frequent network dynamics, and severe resource constraints, it is complex to establish trust in such a network. Mainly, trust systems are vulnerable to attacks that make use of inherent properties of the trust model to alter the accuracy of estimated trust levels, referred to as trust‐distortion attacks. Because of the contradictory nature of such attacks, their detection can be confusing, complex, and energy‐demanding, especially in multiattack environments. To handle such threats, we propose a Green Trust‐distortion Resistant Trust Management Scheme, called GTRTMS, which handles different trust‐distortion attacks in multiattack environments. The proposed solution self‐adapts its trust knowledge monitoring according to the network context to conserve the energy of mobile nodes and reduce the produced CO₂ emissions. Simulation results prove that GTRTMS exhibits significantly better performance than the other counterpart in presence of simultaneous and contradictory different trust‐distortion attacks.     

Simplified life-cycle analysis of PV systems in buildings: present situation and future trends

The integration of photovoltaic (PV) systems in buildings shows several advantages compared to conventional PV power plants. The main objectives of the present study are the quantitative evaluation of the benefits of building-integrated PV systems over their entire life-cycle and the identification of best solutions to maximize their energy efficiency and CO₂ mitigation potential. In order to achieve these objectives, a simplified life-cycle analysis (LCA) has been carried out. Firstly, a number of existing applications have been studied. Secondly, a parametric analysis of possible improvements in the balance-of-system (BOS) has been developed. Finally, the two steps have been combined with the analysis of crystalline silicon technologies. Results are reported in terms of several indicators: energy pay-back time, CO₂ yield and specific CO₂ emissions. The indicators show that the integration of PV systems in buildings clearly increases the environmental benefits of present PV technology. These benefits will further increase with future PV technologies. Future optimized PV roof-integrated systems are expected to have an energy pay-back time of around 1·5 years (1 year with heat recovery) and to save during their lifetime more than 20 times the amount of CO₂ emitted during their manufacturing (34 times with heat recovery). © 1998 John Wiley & Sons, Ltd.     

Thermoelectrics: Impacts on the Environment and Sustainability

Energy saving in power generation, industry, transport, and residential applications by using waste heat with thermoelectrics (TE) may be important for an environmentally sound and sustainable energy system. It is probable that operable TE generators (TEG) will be developed for numerous applications and will save energy and reduce CO₂ emissions from plants. However, the environmental profile of a technology is not sufficiently described by just the energy and CO₂ inputs and outputs of the core process. Necessary preceding and subsequent processes, other environmental impacts, and competing technologies have to be considered as well. Furthermore, sustainability covers aspects beyond environmental soundness. So far, comprehensive studies on TE and the environment/sustainability have not been available. In this paper, the following selected aspects are discussed: resource availability, specific energy consumption of TEG production, specific energy and CO₂ savings in different application fields by TE and competing technologies, and the global potential of TE.     

Mo2C/CNT: An Efficient Catalyst for Rechargeable Li–CO2 Batteries

The rechargeable Li–CO₂ battery is a novel and promising energy storage system with the capability of CO₂ capture due to the reversible reaction between lithium ions and carbon dioxide. Carbon materials as the cathode, however, limit both the cycling performance and the energy efficiency of the rechargeable Li–CO₂ battery, due to the insulating Li₂CO₃ formed in the discharge process, which is difficult to decompose in the charge process. Here, a Mo₂C/carbon nanotube composite material is developed as the cathode for the rechargeable Li–CO₂ battery and can achieve high energy efficiency (77%) and improved cycling performance (40 cycles). A related mechanism is proposed that Mo₂C can stabilize the intermediate reduction product of CO₂ on discharge, thus preventing the formation of insulating Li₂CO₃. In contrast to insulating Li₂CO₃, this amorphous Li₂C₂O₄‐Mo₂C discharge product can be decomposed below 3.5 V on charge. The introduction of Mo₂C provides an effective solution to the problem of low round‐trip efficiency in the Li–CO₂ battery.     

Identifying Active Sites of Nitrogen‐Doped Carbon Materials for the CO2 Reduction Reaction

Nitrogen‐doped carbon materials are proposed as promising electrocatalysts for the carbon dioxide reduction reaction (CRR), which is essential for renewable energy conversion and environmental remediation. Unfortunately, the unclear cognition on the CRR active site (or sites) hinders further development of high‐performance electrocatalysts. Herein, a series of 3D nitrogen‐doped graphene nanoribbon networks (N‐GRW) with tunable nitrogen dopants are designed to unravel the site‐dependent CRR activity/selectivity. The N‐GRW catalyst exhibits superior CO₂ electrochemical reduction activity, reaching a specific current of 15.4 A g_catalyst^?1 with CO Faradaic efficiency of 87.6% at a mild overpotential of 0.49 V. Based on X‐ray photoelectron spectroscopy measurements, it is experimentally demonstrated that the pyridinic N site in N‐GRW serves as the active site for CRR. In addition, the Gibbs free energy calculated by density functional theory further illustrates the pyridinic N as a more favorable site for the CO₂ adsorption, *COOH formation, and *CO removal in CO₂ reduction.     

Structure–Thermodynamic‐Property Relationships in Cyanovinyl‐Based Microporous Polymer Networks for the Future Design of Advanced Carbon Capture Materials

Nitrogen‐rich solid absorbents, which have been immensely tested for carbon dioxide capture, seem until this date to be without decisive molecular engineering or design rules. Here, a family of cyanovinylene‐based microporous polymers synthesized under metal‐catalyzed conditions is reported as a promising candidate for advanced carbon capture materials. These networks reveal that isosteric heats of CO₂ adsorption are directly proportional to the amount of their functional group. Motivated by this finding, polymers produced under base‐catalyzed conditions with tailored quantities of cyanovinyl content confirm the systematical tuning of their sorption enthalpies to reach 40 kJ mol^?1. This value is among the highest reported to date in carbonaceous networks undergoing physisorption. A six‐point‐plot reveals that the structure–thermodynamic‐property relationship is linearly proportional and can thus be perfectly fitted to tailor‐made values prior to experimental measurements. Dynamic simulations show a bowl‐shaped region within which CO₂ is able to sit and interact with its conjugated surrounding, while theoretical calculations confirm the increase of binding sites with the increase of Ph? C?C(CN)? Ph functionality in a network. This concept presents a distinct method for the future design of carbon dioxide capturing materials.     

Atomic Ni Anchored Covalent Triazine Framework as High Efficient Electrocatalyst for Carbon Dioxide Conversion

Electrochemically driven carbon dioxide (CO₂) conversion is an emerging research field due to the global warming and energy crisis. Carbon monoxide (CO) is one key product during electroreduction of CO₂; however, this reduction process suffers from tardy kinetics due to low local concentration of CO₂ on a catalyst's surface and low density of active sites. Herein, presented is a combination of experimental and theoretical validation of a Ni porphyrin‐based covalent triazine framework (NiPor‐CTF) with atomically dispersed NiN₄ centers as an efficient electrocatalyst for CO₂ reduction reaction (CO₂RR). The high density and atomically distributed NiN₄ centers are confirmed by aberration‐corrected high‐angle annular dark field scanning transmission electron microscopy and extended X‐ray absorption fine structure. As a result, NiPor‐CTF exhibits high selectivity toward CO₂RR with a Faradaic efficiency of >90% over the range from ?0.6 to ?0.9 V for CO conversion and achieves a maximum Faradaic efficiency of 97% at ?0.9 V with a high current density of 52.9 mA cm^?2, as well as good long‐term stability. Further calculation by the density functional theory method reveals that the kinetic energy barriers decreasing for *CO₂ transition to *COOH on NiN₄ active sites boosts the performance.     

To Stabilize Oxygen on In/In2O3 Heterostructure via Joule Heating for Efficient Electrocatalytic CO2 Reduction

The regulation of interfacial chemistry for the electrocatalytic reduction of CO₂ into valuable fuels is highly promising but still challenging. Herein, an advanced strategy is developed to modulate the interfacial oxygen species on the hierarchical indium oxide nanosheets. The rapid Joule heating to an elevated temperature is demonstrated to stabilize oxygen species against the electrochemical reduction. Thus, the formation of heterogeneous interface with desirable oxygen species enables to improve electrocatalytic performance. Typically, the obtained electrocatalysts display the high Faradaic efficiency of 94% for carbon dioxide reduction (CO₂RR) into formate and ≈100% for C1 products in the wide potential range from −0.5 to −1.0 V, outperforming most of the state-of-art indium-based catalysts. The in situ experimental characterization and theoretical calculation reveal that the heterointerface with stable In O species would regulate the d-band center to optimize the electronic structure and thus accelerate the protonation process from bicarbonate species adsorbed, leading to the enhanced performance. With the fundamental understanding, the solar-driven CO₂-H₂O cell is constructed to achieve a good energy conversion efficiency of 13.4%. This study offers a feasible strategy to modulate the interfacial structures and properties toward the rational design of advanced electrocatalysts.