The photohydrogen-ion air purifier leverages PHT photohydrogen-ion technology. Under the controlled action of a broad-spectrum photon generator and a proprietary special-metal catalytic medium, it produces hydroxyl ions, superoxide ions, hydrogen peroxide, and pure negative oxygen ions. Upon completion of the purification process, the purified gases are rapidly reduced back into oxygen and hydrogen, leaving no chemical residues and generating no secondary pollutants. The device can be installed in the supply-air main ducts, return-air main ducts, or intermediate sections of centralized ventilation systems and central air-conditioning units; it can also be mounted in the exhaust sections of such systems—for example, in hospitals, chemical laboratories, and virology labs—to achieve centralized indoor air purification and prevent the release of harmful, virus-laden, or other hazardous gases into the atmosphere.