As　the　inverse-opal　structure　facilitates　the　separation　of　electron-hole　pairs　and　electron　transfer,　it　may　generate　many　radical　species　with　strong　oxidation　capability.　When　a　low　bias　voltage　was　applied　on　the　TiO　2　electrodes　with　inverse-opal　structure,　they　exhibited　more　excellent　photoelectrochemical　properties　and　photoelectrocatalytic　activity　than　TiO　2　film　under　simulated　solar　light　irradiation.　When　different　types　of　active　species　scavengers　were　added,　the　different　performances　of　TiO　2　photonic　crystals　in　rhodamine　B　degradation　showed　that　besides　OH　and　holes,　which　were　the　main　active　species　in　the　photocatalysis,　O　2　-　played　a　vital　role　in　the　photoelectrocatalytic　degradation　process.　Furthermore,　the　stronger　signal　of　OH-trapping　photoluminescence　and　the　variation　in　the　concentration　of　nitroblue　tetrazolium　reflected　that　more　OH　and　O　2　-　could　be　generated　in　the　photoelectrocatalysis　than　that　in　the　photocatalysis,　and　O　2　-　was　partially　obtained　from　the　cathode　surface.　At　last,　the　roles　active　species　played　in　the　photoelectrocatalytic　and　photocatalytic　processes　were　compared,　and　the　possible　degradation　mechanisms　of　TiO　2　photonic　crystals　in　photoelectrocatalytic　and　photocatalytic　systems　were　put　forward,　which　could　provide　a　good　insight　into　the　mechanism　of　photoelectrocatalytic　degradation　on　TiO　2　photonic　crystals.　This　journal　is　©　the　Partner　Organisations　2014.