A system for high-temperature reversible electrolysis of water, characterised in that it includes: a high-temperature reversible electrolyser, configured to operate in SOEC (solid oxide electrolyser cell) mode to produce hydrogen and store electricity, and/or in SOFC (solid oxide fuel cell) mode to withdraw hydrogen and produce electricity; a hydride tank, thermally coupled with the reversible electrolyser, the system being configured to allow the recovery of heat released by the hydride tank during hydrogen absorption in order to produce pressurised steam intended for entering the reversible electrolyser in SOEC mode, and to allow the recovery of heat released by the one or more outgoing streams from the reversible electrolyser in SOFC mode so as to allow the desorption of hydrogen from the hydride tank.

A system for high-temperature reversible electrolysis of water, characterised in that it includes: a high-temperature reversible electrolyser, configured to operate in SOEC (solid oxide electrolyser cell) mode to produce hydrogen and store electricity, and/or in SOFC (solid oxide fuel cell) mode to withdraw hydrogen and produce electricity; a hydride tank, thermally coupled with the reversible electrolyser, the system being configured to allow the recovery of heat released by the hydride tank during hydrogen absorption in order to produce pressurised steam intended for entering the reversible electrolyser in SOEC mode, and to allow the recovery of heat released by the one or more outgoing streams from the reversible electrolyser in SOFC mode so as to allow the desorption of hydrogen from the hydride tank.

Electrochemical conversion of CO.sub.2 to formic acid or a salt thereof, using an indium containing catalytic electrode, comprising (a) electrochemically converting CO.sub.2 to formic acid or a salt thereof by applying a voltage to an electrochemical cell comprising the catalytic electrode as cathode and an anode, wherein the electrochemical cell is fed with an electrolyte comprising CO.sub.2; and (b) regenerating the catalytic electrode by lowering the voltage and subsequently washing the catalytic electrode with an aqueous liquid and exposing the catalytic electrode to air without applying voltage; and (c) optionally repeating steps (a) and (b).

Electrochemical conversion of CO.sub.2 to formic acid or a salt thereof, using an indium containing catalytic electrode, comprising (a) electrochemically converting CO.sub.2 to formic acid or a salt thereof by applying a voltage to an electrochemical cell comprising the catalytic electrode as cathode and an anode, wherein the electrochemical cell is fed with an electrolyte comprising CO.sub.2; and (b) regenerating the catalytic electrode by lowering the voltage and subsequently washing the catalytic electrode with an aqueous liquid and exposing the catalytic electrode to air without applying voltage; and (c) optionally repeating steps (a) and (b).

An alkaline electrolyser device for hydrogen production includes a first and a second electric charge battery substantially identical. Each electric charge battery has a first electrode of copper, silver or their alloys, coated with zinc, a second electrode with a ferrous catalyst, and an alkaline aqueous solution in which the first and second electrodes are immersed. An output opening placed in correspondence of the second electrode is suitable to allow the escape from the battery of gases which develop in correspondence of the second electrode. The batteries are short-circuited with an electric power supply member placed between the first or the second electrodes, with a predefined polarity such that the voltage across the electrodes is higher than 1.3 V. In this configuration, the first battery undergoes a discharging process producing hydrogen gas, whilst, contextually, the second battery undergoes a charging process generating oxygen gas. When the discharge cycle of the first battery is completed, the polarity of the electric power supply is inverted, so that the second battery begins to discharge producing hydrogen gas and, at the same time, the first battery recharges producing oxygen gas. The polarity inversion is repeated cyclically so that oxygen and hydrogen are produced alternately in the two batteries.

An alkaline electrolyser device for hydrogen production includes a first and a second electric charge battery substantially identical. Each electric charge battery has a first electrode of copper, silver or their alloys, coated with zinc, a second electrode with a ferrous catalyst, and an alkaline aqueous solution in which the first and second electrodes are immersed. An output opening placed in correspondence of the second electrode is suitable to allow the escape from the battery of gases which develop in correspondence of the second electrode. The batteries are short-circuited with an electric power supply member placed between the first or the second electrodes, with a predefined polarity such that the voltage across the electrodes is higher than 1.3 V. In this configuration, the first battery undergoes a discharging process producing hydrogen gas, whilst, contextually, the second battery undergoes a charging process generating oxygen gas. When the discharge cycle of the first battery is completed, the polarity of the electric power supply is inverted, so that the second battery begins to discharge producing hydrogen gas and, at the same time, the first battery recharges producing oxygen gas. The polarity inversion is repeated cyclically so that oxygen and hydrogen are produced alternately in the two batteries.

The present invention relates to the application of high electrical conductivity electrodes in whatever type of the electrolysis of water to produce hydrogen to substantially reduce power consumption. The high electrical conductivity electrodes are selected from copper electrodes or graphene electrodes and are coated with a catalyst. Type of electrolysis may be conventional diaphragm or membrane type, diaphragm-less or Unipolar electrolysis of water to produce hydrogen.

To enable stable and efficient production of hydrogen. A hydrogen production apparatus according to an embodiment includes an electrolytic unit and an electrolysis power controller. The electrolytic unit produces hydrogen by electrolyzing steam using electric power supplied from an electric power source. The electrolysis power controller controls the supply of electric power from the electric power source to the electrolytic unit. Here, the electrolysis power controller determines whether an unsupplied time during which electric power from the electric power source to the electrolytic unit is not supplied exceeds a predetermined set time, and starts the supply of electric power from the electric power source to the electrolytic unit when the unsupplied time exceeds the set time.

To enable stable and efficient production of hydrogen. A hydrogen production apparatus according to an embodiment includes an electrolytic unit and an electrolysis power controller. The electrolytic unit produces hydrogen by electrolyzing steam using electric power supplied from an electric power source. The electrolysis power controller controls the supply of electric power from the electric power source to the electrolytic unit. Here, the electrolysis power controller determines whether an unsupplied time during which electric power from the electric power source to the electrolytic unit is not supplied exceeds a predetermined set time, and starts the supply of electric power from the electric power source to the electrolytic unit when the unsupplied time exceeds the set time.

Various examples are directed to a solar power electrolyzer system comprising a first electrolyzer stack, a second electrolyzer stack, a first converter and a first converter controller. The first electrolyzer stack may be electrically coupled in series with a photovoltaic array. The first converter may be electrically coupled in series with the first electrolyzer stack and electrically coupled in series with the photovoltaic array. The second electrolyzer stack electrically may be coupled at an output of the first converter. The first converter controller may be configured to control a current gain of the first converter.