Alkaline electrolysis is an electrolysis process with an alkaline (i.e. basic) solution as the electrolyte between the electrodes. In alkaline water electrolysis for the production of hydrogen, potassium hydroxide or sodium hydroxide solution is usually used as the electrolyte. To prevent the product gases from mixing, the electrode compartments are separated by a gas-tight membrane, a so-called diaphragm, which is permeable for the transport of hydroxide ions. Alkaline electrolysis is the most established process for water electrolysis and is characterized above all by the high purity of the product gases.
Under normal conditions, ammonia is a pungent-smelling, colourless, water-soluble and toxic gas that is used as a raw material for a variety of products such as fertilizers and medicines. Ammonia is produced from nitrogen and hydrogen in the Haber-Bosch process. Currently, the hydrogen used is usually produced from natural gas by steam reforming, which releases CO2 emissions. Due to the high demand for ammonia, the Haber-Bosch process is responsible for around two percent of global consumption of fossil fuels. The hydrogen required can gradually be replaced by renewably produced hydrogen from electrolysers in order to operate this process sustainably and without any impact on the climate. Due to the good availability of nitrogen (air) and the higher energy density compared to hydrogen, ammonia is also being discussed as an energy source and (due to the existing infrastructure) as a transport medium for hydrogen.
Without the natural greenhouse effect, life on earth would not be possible – however, human influence has permanently disrupted this system, so that we speak of man-made global warming. The main reason for the increase in greenhouse gas concentrations in the atmosphere caused by humans is the burning of fossil fuels such as coal, oil and natural gas.
In a fuel cell, the chemical reaction energy of a continuously supplied fuel and an oxidizing agent is converted into electrical energy. In everyday usage, the term fuel cell is often used synonymously with hydrogen-oxygen fuel cell. However, in addition to hydrogen, many other fuels can also be used, in particular methanol, butane or natural gas. A fuel cell is not an energy storage device, but a converter. The energy is supplied in chemically bound form.
Hydrogen is assigned different colors depending on the climate impact of its production. CO2 is emitted during the production of gray hydrogen, which is based on fossil fuels. Blue hydrogen is produced using the same process, whereby the resulting CO2 is sequestered or extracted and therefore does not enter the atmosphere. Green hydrogen is produced by electrolysis from renewable energy sources and is therefore hardly associated with CO2 emissions.
Carbon capture and storage (CCS) refers to a group of technologies in which carbon dioxide is captured from exhaust gases, for example from cement production, and injected into underground layers for long-term storage. The pyrolysis of biomass and subsequent storage also removes CO2 from the natural carbon cycle and can be understood as CCS.
Carbon capture and utilization (CCU) refers to the capture of carbon dioxide, particularly from combustion exhaust gases, and its subsequent use as a raw material for chemical or biological processes or directly, e.g. in greenhouses. This extends the use of carbon to a complete circular economy.
-> see emissions trading
Electrolysis process for producing the important basic chemicals chlorine, caustic soda and hydrogen from an aqueous saline solution. To prevent the products from mixing, the electrode compartments are separated. The most relevant separation processes are the diaphragm, amalgam and membrane processes. Chlor-alkali electrolysis is one of the most important chemical processes in industry, accounting for around 2.5 % of the net electricity generated in Germany alone.
Unit of measurement for the climate impact of greenhouse gases, converted to the effect of CO2. By converting to CO2 equivalents (CO2e), different emissions can be better compared in terms of their climate impact. Methane (CH4), for example, has a 28-fold greater climate impact than CO2, so that 1 kg of methane corresponds to 28 kg of CO2e. For nitrous oxide (N2O), this value is 265.
Describes the maximum remaining amount of CO2e that can be released into the atmosphere by humanity in order to maintain a realistic chance of meeting the two-degree target. In order to stay within the CO2 budget, emissions from the combustion of fossil fuels must be drastically reduced and processes must be made more efficient. It may also be necessary to remove CO2 or other greenhouse gases from the atmosphere in order to compensate for unavoidable emissions from agriculture and industry.
Power plants and industrial processes in which CO2 is emitted in large quantities and high concentrations. These point sources are particularly suitable for the application of CCU/CCS, as the CO2 produced can be captured and utilized/stored directly and with comparatively little effort.
Refers to an ecosystem or geological reservoir that temporarily or permanently absorbs and stores carbon. The term should not be confused with carbon storage. While a reservoir in the narrower sense is static, i.e. it can bind a certain amount of CO2, sinks are dynamic reservoirs. Their storage capacity can grow (e.g. in newly established forests) or shrink. Industrial processes can also be CO2 sinks if they use CO2 as a raw material to manufacture carbon-based products.
Co-electrolysis is a type of electrolysis in which several substances are converted simultaneously with the help of electricity. A much-discussed example is the co-electrolysis of water and CO2. This produces synthesis gas (a mixture of hydrogen and CO). Using electricity generated from renewable sources, an important basic building block for the chemical industry can be produced in order to reduce the use of fossil resources and at the same time utilize excess CO2.
This is currently the most important industrial process for producing hydrogen from carbon-containing energy sources and water. CO2 is always produced as a by-product, which puts steam reforming at a disadvantage compared to water electrolysis using electricity from renewable energy sources. Natural gas is currently the most important raw material; in principle, many hydrocarbons such as light petrol, methanol, biogas or biomass are suitable as starting materials. The efficiency (natural gas to hydrogen) is around 60 to 70 %.
Refers to the conversion of the economy, especially the energy industry, towards a lower turnover of carbon. The aim is to only incorporate carbon into products and not to use it as an energy source. Currently, for example, only around 20% of the crude oil produced is used as a material, with the rest being burned directly to generate electricity, heat and as fuel.
Refers to the splitting of a polymer into its monomers or oligomers, i.e. short-chain polymer units.
emissions that do not originate from a localized source but are distributed and therefore difficult to control.
Refers to a group of technologies with which CO2 can be removed directly from the atmosphere without having to rely on CO2 point sources, as in an industrial environment. This not only avoids CO2 emissions, but also actively reduces the CO2 concentration in the atmosphere. Currently developed technologies for this are reversible adsorption processes, such as amine scrubbing or membrane processes, in which CO2 is separated from the other components of the air. Due to the low concentration of CO2 in the air, these processes are complex and therefore currently still comparatively expensive.
In this cement production process, the starting material, limestone, is indirectly heated and burned. The pure CO2 released in the process is captured and can then be transported and used. As it no longer has to be separated from a waste gas mixture, less energy is required for this process compared to other CO2 capture processes.
Downcycling refers to the recycling of waste. However, in this case, the recycled material is not used for an equivalent application and is subsequently of inferior quality to the original material. Construction waste, for example, is often used as fill material in road construction.
In the DRI process, also known as direct reduction, iron ore (iron oxide) is reduced directly – currently mostly with natural gas, but in future with hydrogen. The hydrogen reacts with the oxygen in the iron ore (iron oxide) and is converted into “direct reduced iron” (DRI), also known as sponge iron. Instead of CO2, the DRI process produces water. For further processing, the sponge iron is melted down together with steel scrap in an electric arc furnace.
Describes the simultaneous occurrence of darkness and a lull in the wind. This weather situation typically occurs in winter and results in lower yields from solar and wind energy combined with seasonally high electricity demand. In order to avoid outages even in an electricity grid fed entirely from renewable energy sources, the following components need to be expanded: new, independent storage solutions, load flexibilization and a technology mix for electricity generation.
Process in which substances are broken down into their components using an electric current. The most important electrolysis processes are used to produce hydrogen, aluminum, chlorine and caustic soda. In particular, water electrolysis for the production of hydrogen using electricity from renewable energy sources is a key component towards a climate-neutral society.
Environmental policy instrument with the aim of reducing pollutant emissions at the lowest possible economic cost. The quantity-oriented system fits the initial problem (CO2 budget). Allocation takes place via the market. In the European Union, emissions trading (ETS) was introduced by law in 2005. The EU ETS currently covers electricity generation and some industrial sectors such as steel and cement production.
The energy balance characterizes the total expenditure for the production, operation and reuse (disposal or recycling) of products. This includes not only energy consumption during production, but also the energy and resources required for production and disposal.
Describes the ratio of product, resource or energy yield (output) to the energy supplied (input). Energy efficiency therefore refers to the rational use of energy. Optimized processes are intended to minimize the quantitative and qualitative losses that occur during the conversion, transport and storage of energy in order to achieve a specified (energy) benefit while reducing the primary or final energy input.
Means maintaining an appropriate, stable and predictable energy supply. The switch from the controllable use of fossil fuels to volatile renewable energy sources such as wind power and photovoltaics is leading to new challenges in the energy market, which must be met with a mix of technologies for the generation and storage of energy as well as load flexibility.
In the context of the energy transition, they are used to store energy that is available but not currently required for later use. Energy is often converted into other forms of energy, such as electrical energy into chemical energy (battery or PtX), which can then be converted back into the desired form for later use if required.
The German Electricity and Gas Supply Act (Energiewirtschaftsgesetz – EnWG) first came into force in 1935 and was last revised in 2005. It contains fundamental regulations on the law governing grid-bound energy. The objectives of the EnWG are to provide the general public with the most secure, affordable, consumer-friendly, efficient and environmentally friendly grid-based supply of electricity and gas and to ensure effective and undistorted competition.
Any type of energy that renews itself through natural processes at a rate that is at least as high as the utilization rate. For example, solar radiation, wind or biological resources.
The German Renewable Energy Sources Act (Erneuerbare-Energien-Gesetz, EEG 2017) regulates the preferential feed-in of electricity from renewable sources into the electricity grid and guarantees their producers fixed feed-in tariffs. Since the 2016/2017 amendment to the EEG, the law has largely switched to the tendering procedure, which aims to achieve specified expansion corridors as cost-effectively as possible. The quantitative restriction of RE expansion under the EEG is the subject of controversial debate.
In 2009, the Renewable Energy Directive set binding targets for the member states of the European Union for the share of renewable energy in total energy demand to be achieved by 2020. The aim was to achieve a share of renewable energy of at least 20 percent throughout the EU. In 2018, a revised Renewable Energy Directive (RED II) was presented, which, among other things, stipulates a mandatory share of renewable energy of 32% by 2030. Among other measures, the directive also stipulates a 14% share of renewable energy in the transport sector. The use of green hydrogen in the refinery process is also to be taken into account here.
Fischer-Tropsch synthesis is a process in which synthesis gas, a mixture of carbon monoxide and hydrogen, is converted into liquid, long-chain hydrocarbons. These hydrocarbons are used as synthetic fuels, motor oils and raw materials for the chemical industry. Conventionally, synthesis gas is obtained from fossil raw materials by gasification; alternatively, however, it can also be produced from CO2 by reaction with hydrogen or co-electrolysis with water to provide the basis for CO2-neutral synthetic fuels.
Carbon-containing energy sources that have been created over millions of years and are therefore non-renewable in human time dimensions. When they are burned, CO2 is released into the atmosphere, which has been sequestered over millions of years.
Climatic effects are complex and regionally dynamic, so that a stronger greenhouse effect can lead to an increase in temperature, but can also lead to cooling locally. In order to measure climate change, it is therefore necessary to use a globally averaged temperature.
The basic materials industry refers to all branches of industry that extract raw materials (e.g. ores, rocks, crude oil, salts, wood) and make them available so that they can be used in the processing industry. As the extraction of resources often requires a lot of energy, there is great potential here for reducing greenhouse gases.
In the Haber-Bosch process, ammonia is produced from nitrogen and hydrogen. Currently, the hydrogen used is produced from natural gas by means of steam reforming, which releases CO2 emissions. Due to the high demand for ammonia, the Haber-Bosch process is responsible for around two percent of global consumption of fossil fuels. The hydrogen required can gradually be replaced by renewably produced hydrogen from electrolysers in order to operate this process sustainably and without any impact on the climate.
High-pressure electrolysis is an electrolysis process under high system pressure. Electrolysis is usually carried out at ambient pressure or moderately increased pressure. An increased process pressure of up to 200 bar is particularly advantageous for water electrolysis, as it eliminates the need for subsequent complex compression of the hydrogen product. Due to the solid electrolyte, PEM electrolysis is better suited to high-pressure electrolysis than alkaline electrolysis.
High-temperature electrolysis is a water electrolysis process that is characterized by a high process temperature of up to 900 °C (in contrast to the usual < 80 °C). The water is therefore supplied as steam. The high temperature improves the reaction kinetics of the electrolysis, which reduces the power requirement. High-temperature electrolysers are usually realized with solid oxide electrolytes (SOEC = Solid Oxide Electrolyser Cell), which is permeable to O2 or H+ ions. The high operating temperature can be provided by waste heat from other processes, for example.
Intergovernmental Panel on Climate Change, often referred to in German as “Weltklimarat”. The main task of the committee is to compile the scientific basis and the global state of research on the effects of climate change and its risks, as well as mitigation and adaptation strategies, and to evaluate them from a scientific perspective.
Catalytic cracking is a chemical process in which organic substances are heated with the aid of a catalyst. The catalytic cracking process is used to split various higher-boiling oil fractions. Climate neutrality Processes or products are climate neutral if they have no impact on climate change – i.e. are not associated with greenhouse gas emissions. In order to limit anthropogenic climate change to an acceptable level, negative emissions may also be necessary (climate-positive measures). Climate neutrality is often used synonymously with greenhouse gas neutrality.
Climate sensitivity is a measure of how sensitively the globally averaged near-surface air temperature on Earth reacts to changes in carbon dioxide concentration. It represents the temperature change that the earth would experience if the CO2 content in the atmosphere doubled and is expressed in degrees Celsius. It is assumed that the climate is in equilibrium before and after the change; in other words, an initial and final state is considered without the gradual warming between the reference points. If, on the other hand, the change in climate up to a certain point in time is considered, this is also referred to as “effective climate sensitivity”.
Carbon dioxide (CO2) is a building block of the global carbon cycle and an important greenhouse gas as a component of the atmosphere. As a result of human activities, in particular the burning of fossil fuels, the concentration of CO2 in the atmosphere has risen from around 280 ppm (parts per million) to around 410 ppm since the beginning of the industrial revolution. The current climate change and the increase in the global mean temperature are largely due to this increase.
The system of chemical transformations of carbon-containing compounds in the global systems of rock, water, atmosphere and biomass as well as the exchange of these compounds between these systems. Knowledge of this cycle, including its sub-processes, makes it possible, among other things, to assess human intervention in the climate and thus its effects on global warming and to react appropriately.
The simultaneous generation of mechanical energy, which is usually converted directly into electricity, and usable heat for heating purposes (district heating or local heating) or for production processes (process heat) in a joint thermodynamic process, usually in a combined heat and power plant.
Describes the ability to use electricity flexibly. The flexible use of electricity in energy-intensive processes is an important component of the energy transition, as it allows the fluctuating electricity production of volatile renewable energy sources (solar, wind) to be buffered in order to avoid overloading the electricity grid and the need for additional energy storage.
A generic term for battery types based on lithium compounds in all three components of the electrochemical cell. Both the materials in the negative and positive electrodes and the electrolyte contain lithium ions. Lithium-ion batteries have a high energy density compared to other battery types, but usually require protective circuits as they can be damaged by deep discharge and overcharging.
Liquid organic hydrogen carriers (LOHC) are used as “carriers” for hydrogen (H2). To do this, they are loaded with hydrogen (hydrogenation). Due to the transportation of H2 is easier than molecular hydrogen and existing infrastructure. At the point of consumption, the compound is then usually dehydrated so that the H2 is freely available again and can be used. The discharged “carrier” can then be reused.
The main component of natural gas and biogas. In the atmosphere, it has a global warming potential 33 times higher than CO2. This makes it the second most important greenhouse gas caused by humans.
A chemical reaction in which carbon monoxide or carbon dioxide is converted into methane with the help of hydrogen. The methane obtained can be fed into the existing natural gas grid, thereby extending the utilization chain of the carbon content.
One of the most widely produced organic chemicals, which serves as the starting point for the production of a wide range of chemical products. Methanol can be produced from CO2 and hydrogen, making it a sustainable entry point into the chemical value chain.
In a direct methanol fuel cell (DMFC), methanol is oxidized to CO2 and water in a controlled reaction with oxygen, generating electricity. As operation is virtually silent and the handling of the liquid fuel (methanol-water mixture) is relatively simple compared to hydrogen, this type of power generation is mainly used for camping, military equipment or remote measuring stations.
Methanol is conventionally synthesized from synthesis gas, a mixture of carbon monoxide and hydrogen. Alternatively, CO2 can also serve as a carbon source in a slightly modified process in order to provide the chemical industry with this important basic chemical in a CO2-neutral way. As the chemical value chain is currently based on fossil resources, the synthesis gas route has so far been more efficient. However, in the transition to a climate-neutral industry, economic operation based on CO2 is also to be expected.
Negative emissions refer to the targeted removal of greenhouse gases, in particular CO2, from the atmosphere, either through the expansion of CO2-absorbing ecosystems or through industrial processes. Industrial processes are based either on the removal of CO2 from the air (direct air capture, enhanced weathering), combined with the binding in products or storage of CO2, or on the utilization of biomass in combination with a storage solution (biochar, BECCS).
These are technologies that aim to remove greenhouse gases from the atmosphere. Examples include direct air capture, pyrolysis CCS, BECCS and enhanced weathering.
In its 2018 report, the Intergovernmental Panel on Climate Change (IPCC) shows that greenhouse gas emissions must be reduced to zero in order to stabilize global temperatures. As there are areas in which these emissions cannot be completely avoided, such as in agriculture or individual industrial sectors, these emissions must be offset in order to cause no net emissions.
Agreement of the 197 parties to the UNFCCC with the aim of climate protection as a successor to the Kyoto Protocol. The agreement, which was adopted in 2015, aims to limit man-made global warming to well below 2 °C compared to pre-industrial levels.
Short for proton exchange membrane or polymer electrolyte membrane electrolysis. A process for water electrolysis with a solid electrolyte, which simultaneously serves to separate the electrode compartments and thus prevents the product gases from mixing. The solid electrolyte is permeable for the transport of H+ ions. The operating power of the PEM electrolysis is highly controllable and therefore particularly suitable for operation with electricity from volatile renewable energy sources. The long-life solid electrolyte means that maintenance requirements are low. PEM electrolysers are currently still operated in comparatively low power ranges.
Is an energy industry concept (or technology) in which hydrogen is produced using electricity in water electrolysis. The power-to-gas concept also includes the possible downstream methanation of CO2. The gas produced in this way can be used as a resource in various industrial sectors, as a fuel for fuel cell vehicles, for example, or as an energy storage solution with subsequent reconversion into electricity.
Refers to various technologies for storing or otherwise using electricity. Power-to-X technologies (also P2X, PtX) are particularly important in times of (future) oversupply from variable renewable energy sources such as solar energy, wind energy and hydropower in order to make efficient use of these supply peaks.
Is the thermal treatment of carbon-containing compounds at 350 to 900 °C in a low-oxygen atmosphere. During this process, three carbonaceous products are produced, which can then be stored in different ways to generate negative emissions: Biochar (used to improve soils, or build up coal deposits), pyrolytic liquid (creosote), pyrolysis gas (can be sent to geological storage as CO2 after combustion).
A type of battery in which the electrical energy is stored in chemical compounds that are dissolved in a solvent and can be circulated and stored in separate circuits. Charging and discharging takes place in a central cell, which determines the maximum output of the battery. The storage capacity, on the other hand, is determined solely by the size of the storage tanks used.
Process component of refineries. Depending on the application, different processes are used for the chemical conversion of usually liquid hydrocarbon fractions (naphtha or pyrolysis oil).
Solvolysis is a special case of chemical depolymerization (often used synonymously in the literature), which can be used in the case of polycondensates (e.g. polyester, polyamides), particularly in the form of hydrolysis (bond cleavage with water as a reactant). Different solvents can be used. In this respect, solvolysis can be further subdivided into glycolysis, methanolysis, hydrolysis and aminolysis.
In the chemical industry, this refers to a mixture of hydrogen and carbon monoxide that can be used flexibly to synthesize a variety of compounds. Currently, synthesis gas is mainly obtained from fossil resources. In the future, however, it can also be obtained renewably from water (electrolysis) and CO2.
Conventional fuels, such as petrol, diesel or kerosene, are produced from crude oil and have a correspondingly poor carbon footprint. Synthetic fuels can have the same properties as conventional fuels, but can be produced from renewable resources, albeit at a comparatively high energy cost.
Global warming caused by greenhouse gases in the atmosphere. Solar radiation causes energy in the form of short-wave radiation to reach the earth through the atmosphere. Long-wave radiation, on the other hand, which is emitted as heat radiation from the earth’s surface and the heated air, cannot pass through the atmosphere unhindered and is partially reflected there by greenhouse gases, resulting in a build-up of heat.
Are infrared-active gases such as water vapor, carbon dioxide (CO2), ozone (O3), dinitrogen (N2O) and methane (CH4), which contribute to the greenhouse effect. They absorb and reflect part of the long-wave infrared radiation emitted by the ground, which would otherwise escape into space, thus causing a build-up of heat in the atmosphere.
A process can be described as greenhouse gas neutral if no greenhouse gas emissions are caused in the process, meaning that it has no impact on the climate. The term can be extended to entire sectors or societies. Greenhouse gas neutrality is often used synonymously with climate neutrality.
Abbreviation for United Nations Framework Convention on Climate Change. The aim of this international agreement concluded in 1992 is to stabilize the concentration of greenhouse gases in the atmosphere at a level that prevents dangerous anthropogenic interference with the climate system. The participating states of the UNFCCC have met annually since 1995 at so-called climate summits to discuss concrete steps to achieve the agreed goal. In 1997, the UNFCCC adopted the Kyoto Protocol, an additional protocol to the Climate Convention. In the Paris Agreement adopted in 2015, all countries are obliged for the first time to define and implement reduction targets and to review their progress. The targets are to be compared with the latest scientific findings and adjusted every five years.
Process-related CO2 quantities that cannot be avoided despite optimization of the production process or product.
A system that uses technical work to absorb thermal energy from a reservoir at a lower temperature (e.g. air or ground) and – together with the drive energy – transfers it as useful heat to a system to be heated at a higher temperature. The mode of operation thus corresponds to the reversal of the power-heat process.
Storage tanks for thermal energy. Heat storage systems can be built in different sizes, ranging from small decentralized systems to large central storage facilities. In addition to storing thermal energy, the most important aim of heat storage systems is to decouple the generation and use of heat over time.
Is considered to be the energy source of the future as it does not cause any harmful emissions, especially carbon dioxide, if it is produced using renewable energies such as wind or sun via water electrolysis. At present (2019), hydrogen is still produced almost exclusively from fossil primary energy, mainly by reforming natural gas. The use of hydrogen produced in this way therefore generates CO2 emissions.
In the hydrogen fuel cell, commonly known as a fuel cell, hydrogen and oxygen react in a controlled manner to form water, which generates electricity. As the overall reaction in the fuel cell corresponds to the combustion reaction, this conversion is also known as “cold combustion”. The reaction taking place here is the reverse of hydrogen electrolysis, where water is split into hydrogen and oxygen with the help of electricity. White certificate White certificates are systems in which market players, mainly energy suppliers and grid operators, are obliged to achieve a specific savings target within a set period and to implement energy efficiency measures for consumers. The certificates verify the energy-saving measures in terms of quantity and time period. For energy savings made, the operator receives corresponding certificates, which it can either use to meet its own obligation or sell to other obligated market players. If an obligated energy supplier or distributor has accumulated no or too few certificates, it faces a penalty fee.
Colloquial German term for the regular assessment reports of the Intergovernmental Panel on Climate Change (IPCC). Every five to seven years, the state of global research on the causes and consequences of climate change as well as options for adaptation and emission reduction are summarized in an editorial process by proven experts.
In everyday usage, no clear distinction is often made between weather and climate, but this is essential for understanding the climate system. Weather is the constantly changing atmospheric condition that we experience on a daily basis and which can only be predicted over short periods of time. Climate, on the other hand, is the average weather over a longer period of time at a specific location. Climate is therefore not directly measurable, but a statistic made up of many measurements.
Describes the efficiency of a technical device or system as a dimensionless ratio or percentage, usually the ratio of useful energy to supplied energy. Efficiency is an important parameter for evaluating processes and storage technologies, particularly in the context of the energy transition and efficient energy use.
The Paris Agreement commits the world’s nations to keeping the increase in global mean temperature to well below 2°C above pre-industrial levels and to making efforts to limit the temperature increase to 1.5°C in order to mitigate the negative effects of climate change and avoid reaching potential tipping points.
Glossary The Power of Hydrogen
Investor-contact
Henriette Siegel
Phone: +49 (381) 79 99 02-320
E-mail: click here
Web: www.ir.h2apex.com
H2APEX Group SCA
19, rue de Flaxweiler
6776 Grevenmacher
Luxemburg
Phone.: + 352 28384720
Fax: + 352 28384729
E-Mail: click here